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ORGANIC 
AGRICULTURAL CHEMISTRY 



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THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CHICAGO • DALLAS 
ATLANTA • SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON • BOMBAY • CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 



ORGANIC 
AGRICULTURAL CHEMISTRY 

( The Chemistry of Plants and Animals} 



A TEXTBOOK 

OF GENERAL AGRICULTURAL CHEMISTRY OR 

ELEMENTARY BIO-CHEMISTRY FOR 

USE IN COLLEGES 



BY 



JOSEPH SCUDDER CHAMBERLAIN, Ph.D. 

PROFESSOR OF ORGANIC AND AGRICULTURAL CHEMISTRY 
IN THE MASSACHUSETTS AGRICULTURAL COLLEGE 



THE MACMILLAN COMPANY 
1916 

All rights reserved 



9>s*s 



c *3 



Copyright, 1916, 
By THE MACMILLAN COMPANY. 



Set up and clectrotyped. Published May, 1916. 




NcrfajaoH ^ress 
S. Cushing Co. — Berwick & Smith Co. 
Norwood, Mass., U.S.A. 



MAY II 1916 
>CI.A431029 



* 

r 



Co 

MY FATHER 
W. I. CHAMBERLAIN 

WHO HAS SPENT HIS LIFE IN AND FOR 

AGRICULTURE, THIS BOOK IS 

LOVINGLY DEDICATED 



Digitized by the Internet Archive 
in 2010 with funding from 
The Library of Congress 



http://www.archive.org/details/organicagricultuOOcham 



PREFACE 

Agricultural chemistry is a subject presenting two quite 
distinct lines of study. The study of soils and fertilizers, includ- 
ing the relation of the plant to its soil food, is almost wholly 
inorganic and physical. On the other hand, the study of plants 
and animals as living organisms is as distinctly organic and 
physiological, embracing the greater part of what is termed Bio- 
chemistry. 

This has led the author to prepare one part of a textbook of 
General Agricultural Chemistry with this distinction in view, 
and to designate it as Organic Agricultural Chemistry — The 
Chemistry of Plants and Animals. The companion volume on 
Inorganic Agricultural Chemistry — The Chemistry of Soils 
and Fertilizers — is being prepared by the author's associate, 
Dr. Ernest Anderson. 

The author believes that there is a place in our Agricultural 
Colleges for a course covering the work included in these two 
volumes with the definite aim of giving to students of practical 
agriculture enough general scientific instruction in chemistry to 
enable them to understand and correlate the broad problems 
of agricultural practice. The course covered by the two books 
has been planned to follow a course in general chemistry such 
as is given in the Freshman year in most colleges, and assumes 
a knowledge represented by such work. 

The present volume does not pretend in any sense to re- 
place the more thorough study of both organic and physiological 
chemistry by those students preparing to be chemists or other 
scientific workers in agriculture. Assuming that the student 
has not had a special course in systematic organic chemistry, 
there is included, as Section I, the essentials of such a study as 
related directly to agriculture. Following this systematic study 
of organic chemistry the treatment in Section II is largely 



VL11 PREFACE 

physiological, and centers around the general subjects of food 
and nutrition as applies to both animals and plants and photo- 
synthesis in plants. In the last section on Crops, Foods and 
Feeding the effort has been to present the chemical basis for 
the valuation of animal foods, but without entering into the dis- 
cussion of the practical operation and results of animal feeding. 

In presenting the physiological chemistry of plants and ani- 
mals a departure has been made from the usual custom, and the 
detailed study of animals and animal nutrition is considered 
before that of plants. The author believes that this procedure 
presents bio-chemistry in such a way that the student gains the 
correct view of plants and animals as living organisms. It also 
emphasizes the real differences between these two forms while 
retaining the idea of fundamental similarity. 

There has been no effort to make the book a handbook of 
facts in regard to the subjects treated, and it is not a textbook 
of agricultural analysis, the methods mentioned being consid- 
ered only as to the fundamental principles. The presentation is 
general and is in the lecture style with the underlying purpose 
of making a book of the most value to students as a text for 
class use. Laboratory experiments have been incorporated in 
the text as this has seemed to be desirable. Except in connec- 
tion with the tables practically no references to literature have 
been cited, but at the end of each section a list is given of 
reference books which cover the subjects discussed. The author 
wishes to give full credit to all of these books as sources of the 
material presented. 

The book is the result of five years' experience in giving a 
course in general agricultural chemistry to students in practical 
agriculture and horticulture in the Massachusetts Agricultural 
College, the work in the present volume being carried in a 
course of two lectures and one laboratory per week for one 
semester. 

While intended primarily for use in Agricultural Colleges, the 
author hopes that the book may be found of value in other 
colleges where an elementary presentation of bio-chemistry is 
desired. 



PREFACE ix 

Finally the author wishes to acknowledge the assistance and 
cooperation of his associate, Dr. Ernest Anderson, and of all 
others who have in any way aided him in the work. 

JOSEPH S. CHAMBERLAIN. 

Massachusetts Agricultural College, 

Amherst, Massachusetts. 

November 15, 1915. 



TABLE OF CONTENTS 



PAGES 

Introduction 1-2 



SECTION I. SYSTEMATIC . 3 

Chapter I. Hydrocarbons 5-17 

Experiment Study I ; Hydrocarbons from wood and coal, 
7. Methane, 7. Occurrence, properties, constitution, 7, 8. 
Structural formula, 8. Experiment Study II; Methane, 9. 
Substitution, 10. Synthesis of higher hydrocarbons, 13. 
Isomerism, 15. 

Chapter II. Substitution Products of the Hydrocarbons 18-41 
Halogen compounds, 18. Chloroform, iodoform, carbon 
tetrachloride, 18. Experiment Study III; Halogen sub- 
stitution products, 19. Halogen ethanes, 19. Isomerism of 
di-brom-ethane, 20. Cyanides and amines, 21. Cyanamide, 
23. Calcium cyanamide, 23. Experiment Study IV ; Cyan- 
ides, 25. Hydroxy substitution products or alcohols, 25. 
Alcohol series, 26. Experiment Study V; Distillation of 
alcohols, Fractional distillation, 26. Table I; Alcohol per 
cent and specific gravity, 28. Methyl alcohol, 29. Experi- 
ment Study VI; Methyl alcohol, 30. Ethyl alcohol, 31. 
Experiment Study VII; Ethyl alcohol, 31. Alcoholic fer- 
mentation, 32. Enzymes, zymase, 33. Experiment Study 
VIII ; Alcoholic fermentation, 34. Diastase, 34. Absolute 
alcohol, 36. Alcoholic beverages, 36. Industrial uses, 37. 
Taxation, 37. Denatured alcohol, 38. Higher alcohols, 39. 
Experiment Study IX; Amyl alcohol, 40. Polyhydroxy 
alcohols, 40. Glycol, 40. Glycerol, 41. Higher poly- 
hydroxy alcohols, 41. 

Chapter HI. Oxidation Products of Alcohols . . . 42-53 
Aldehydes, 42. Formaldehyde (formalin), 43. Acetalde- 
hyde, 44. Aldehyde reactions; addition compounds, oximes, 



Xll TABLE OF CONTENTS 



hydrazones, 44. Experiment Study X; Aldehydes, 45. 
Acids, 46. Acetic acid series, 47. Formic acid, 48. Ex- 
periment Study XI; Formic acid, 48. Acetic acid, 49. 
Glacial acetic acid, 49. Vinegar, 50. Experiment Study 
XII; Acetic acid and vinegar, 51. Polycarboxy acids, 51. 
Oxalic acid, 52. Experiment Study XIII; Oxalic acid, 53. 
Succinic acid, 53. 

Chapter IV. Derivatives of Alcohols and Acids . . 54-65 

Ethers, 54. Ethyl ether, 54. Experiment Study XIV; 
Ether, 55. Acid chlorides and acid amides, 55. Esters, 56. 
Simple esters, 56. Fruit flavors, 56. Fats, oils and waxes, 

57. Fatty acids, 57. Glycerol esters, 58. Esterification, 

58. Hydrolysis, 59. Soap, 60. Saponification, 60. Im- 
portant fats and oils, 60. Physical constants, 61. Chemical 
constants, 61. Table II; Fats and oils, 62. Experiment 
Study XV; Esters, 62. Experiment Study XVI; Fats and 
soap, 63. 

Chapter V. Mlxed Compounds 66-81 

Halogen-aldehydes, 66. Tri-chlor-aldehyde, chloral, 66. 
Halogen- acids, 67. Hydroxy-acids, 67. Lactic acid, 68. 
Stereoisomerism, 69. Optical activity, 69. Asymmetric 
carbon, 71. van't Hoff-Le Bel, 71. Tetrahedral theory, 
72. Inactive lactic acid, 73. Dextro lactic acid, 74. Levo 
lactic acid, 74. Malic acid, 75. Tartaric acid, 76. Cream 
of tartar, 76. Rochelle salt, 77. Tartar emetic, 77. Stereo- 
isomerism of tartaric acid, 78. Dextro-, levo-, racemic- and 
meso-tartaric acids, 78. Citric acid, 80. Experiment Study 
XVII ; Lactic, malic, tartaric and citric acids, 80. 

Chapter VI. Amino-acids, Proteins, Urea, Uric Acid . 82-103 

Amino-acids, 82. Glycine, 84. Hippuric acid, 84. 
Alanine, 85. Higher amino-acids, 85. Proteins, 87. 
Physical properties, 88. Chemical properties, 90. Com- 
position, 90. Analysis, 90. Kjeldahl method, 90, 93. 
Molecular weight, 90. Hydrolytic decomposition, 91. 
Polypeptides, 92. Experiment Study XVIII; Proteins, 93. 
Urea, uric acid and purine bases, 97. Urea, 97. Biuret, 101. 
Experiment Study XIX; Urea, 101. Uric acid and purine 
bases, 102. Xanthine, caffeine, theobromine, 103. 



TABLE OF CONTENTS Xlll 

PAGES 

Chapter VII. Carbohydrates 104-136 

Composition, 104. Experiment Study XX ; General prop- 
erties of carbohydrates, 105. Constitution, 105. Classifica- 
tion, 107. Trioses, 109. Pentoses, no. Experiment Study 
XXI; Pentosans and pentoses, no. Hexoses, no. Glu- 
cose, in. Determination, in. Fermentation of glucose, 
113. Fructose, 113. Galactose, 114. Experiment Study 
XXII; Hexoses, 114. Disaccharoses, 115. Sucrose or cane 
sugar, 115. Hydrolysis, 117. Inversion, 117. Invert sugar, 
117. Sugar analysis, 118. Maltose or malt sugar, 118. 
Lactose or milk sugar, 119. Experiment Study XXIII; 
Disaccharoses, 120. Polysaccharoses, 120. Hydrolysis, 120. 
Source of alcohol, 121. Starch, 121. Hydrolysis, 122. 
Source of glucose, 123. Determination, 123. Experiment 
Study XXIV; Starch, 123. Dextrin, Glycogen, 124. Inulin, 
Cellulose, 125. Paper, 126. Mercerized cotton and arti- 
ficial silk, 127. Explosives and celluloid, 127. Experiment 
Study XXV; Cellulose, 128. Table III; Summary of car- 
bohydrates, 129. Unsaturated compounds, 130. Con- 
clusion, 134. References to Section I, 135. 



SECTION II. PHYSIOLOGICAL . . 137 

Chapter VIII. Enzymes and Enzymatic Action . . . 139-145 
Enzymes and fermentation, 139. Definition, 140. Gen- 
eral nature of enzymes, 140. Reactions brought about by 
enzymes, 141. Hydrolyzing enzymes, 141. Oxidizing 
enzymes, 142. Reducing enzymes, 142. Coagulating en- 
zymes, 142. Decomposing and splitting enzymes, 142. 
Character of enzyme action, 142. Specific, 142. Reversible, 
143. Zymogens, 143. Co-enzymes and anti-enzymes, 144. 
Names of enzymes, 144. Table IV; Enzymes, 145. 

Chapter IX. Composition of Plants and Animals . . 146-153 
Organic and inorganic constituents, 146. Volatile and non- 
volatile constituents, 147. Ash, 149. Table V; Volatile 
and nonvolatile constituents, 150, 151. Experiment Study 
XXVI; Organic and inorganic constituents, 152. 

Chapter X. The Living Cell and its Food . . . 154-158 
Plant and animal cell alike, 154. Composition of the cell, 
154. Cell energy and cell food, 155. Food as energy ma- 



XIV TABLE OF CONTENTS 



terial, 155. Oxidation of food, 156. Heat and work, 156. 
Food as building material, 157. Function of food, 157. 
Plants and animals compared, 157. 

Chapter XI. Animal Food and Nutrition; Digestion and 

Absorption 159-189 

Animal food, 159. Definition, 159. Utilization of food, 
160. Mastication, 161. Digestion, 162. Digestive region, 
163. Digestion of carbohydrates, 163. Monosaccharoses, 
final product of digestion, 164. Hydrolysis of di- and poly- 
saccharoses, 164. The mouth, 165. Saliva, 165. Enzymes 
of saliva, 166. Ptyalin and maltase, 166. Conditions of 
salivary action, 167. Salts in saliva, 167. Organic com- 
pounds in saliva, 168. Experiment Study XXVII ; Salivary 
digestion, 168. The stomach, 169. The small intestine, 
170. Pancreatic juice, amylopsin, 170. Intestinal juice, 
170. Sucrase, maltase and lactase, 171. Digestion of pro- 
teins, 171. The stomach, 172. Gastric juice, 172. Rennin, 
173. Pepsin, 173. Hydrochloric acid, 173. Experiment 
Study XXVIII; Gastric digestion, 174. The small intes- 
tine, 175. Pancreatic juice, 176. Hormones, 176. Pan- 
creatic rennin, 177. Trypsin, 177. Trypsinogen, 177. 
Enterokinase, 177. Intestinal juice, 178. Erepsin, 178. 
Digestion of fats, 179. Hydrolysis of fats, 179. The 
stomach, gastric lipase, 180. The small intestine, pancreatic 
lipase, 180. The bile, 181. The large intestine, 182. Ab- 
sorption of food, 183. Absorption of carbohydrates, 183. 
Absorption of proteins, 184. Absorption of fats, 185. Re- 
sume of digestion and absorption, 186. Time for food pas- 
sage, 188. 

Chapter XII. Animal Food and Nutrition; Metabolism 190-208 
Metabolism, Anabolism, Katabolism, 190. Metabolism 
of carbohydrates, 191. Direct metabolism, 191. Glycogen, 
192. Conversion of glycogen into glucose, 192. Amount of 
glycogen in the liver, 192. Oxidation of glucose, 193. 
Muscle glycogen, 194. Conversion of carbohydrates into 
fats, 195. Feeding experiments, 195. Respiratory quotient, 
196. Metabolism of fats, 198. Body fat and milk fat, 199. 
Conversion of fats into carbohydrates, 200. Metabolism of 
proteins, 201. Amino-acids, 201. Polypeptide nucleus, 202. 
Serum albumin, 202. Body protein, 203. Oxidation of pro- 
tein, 203. Katabolism of protein, 204. Katabolic products, 



TABLE OF CONTENTS 



XV 



204. Nitrogen excretion in urine, 205. Formation of urea, 
etc., 205. Conversion of proteins into carbohydrates, 206. 
Conversion of proteins into fats, 207. 

Chapter XIII. Milk, Blood and Urine .... 209-231 
Milk, 209. Constituents, 209. Carbohydrates, 209. 
Fats, 210. Proteins, 211. Casein, 212. Lactalbumin, 212. 
Inorganic salts, 212. General properties, 214. Analysis, 
215. Preservatives, 216. Butter, 216. Cheese, 217. 
Whey, 217. Food value, 218. Experiment Study XXIX; 
Milk, 218. Blood, 219. Properties, 220. Constituents, 
220. Erythrocytes, 220. Haemolysis and haemagglutina- 
tion, 220. Haemoglobin and oxyhaemoglobin, 221. Leu- 
cocytes, 222. Blood plasma, 223. Blood serum, 223. 
Serum albumin, 224. Fibrinogen and fibrin, 224. Clotting, 
224. Experiment Study XXX; Blood, 226. Urine, 226. 
Constituents, 227. Nitrogen compounds, 227. Urea, 227. 
Isolation and determination, 227. Uric acid, 228. Crea- 
tinine, 228. Ammonia, 228. Hippuric acid, 229. Patho- 
logical constituents, 229. Glucose, 229. Albumin, 230. 
General properties, 230. Experiment Study XXXI ; Urine, 
231. 

Chapter XIV. Plant Physiology 232-258 

Plants and animals compared, 232. Similarity, 232. 
Differences, 235. Exothermic and endothermic reactions, 

235. Animals liberate energy, 236. Plants store energy, 

236. Photosynthesis, 237. Source of energy, 237. Chlo- 
rophyll bodies and chlorophyll, 238. Products of photo- 
synthesis, 238. Function of products of photosynthesis, 241. 
Carbohydrates, 241. Carbohydrates present in plants, 242. 
Metabolic transformations, 242. Sugars, 243. Transloca- 
tion material, 243. Cell food, 243. Starch, 244. Reserve 
food, 244. Diastase and maltase, 244. Germination, 245. 
Experiment Study XXXII; Diastase and starch, 246. 
Building material, 246. Cell wall, 247. Cellulose, 247. 
Fats and proteins, 248. Synthesis of fats and proteins, 248. 
Location of fats, 249. Location of proteins, 249. Source of 
nitrogen, 249. Nitrogen cycle, 250. Fixation of atmospheric 
nitrogen, 251. Metallic nitrides, 251. Electrical discharges, 
251. Nodule bacteria, 252. Reactions of nitrogen cycle, 
254. Diagram of nitrogen cycle, 255. Resume, 255. Ref- 
erences to Section II, 257. 



XVI TABLE OF CONTENTS 



PAGES 

SECTION III. CROPS, FOODS AND FEEDING 259 

Chapter XV. Occurrence and Uses of Important Con- 
stituents in Agricultural Plants 261-276 

Carbohydrates, 261. Cellulose, 262. Forms of cellulose, 
262. Normal celluloses, 262. Hemicelluloses, 263. Ligno- 
celluloses, 264. Pectocelluloses, 264. Cellulose as food, 265. 
Crude fiber, 265. Table VI ; Cellulose content of crops, 266. 
Experiment Study XXXIII ; Cellulose and crude fiber, 267. 
Starch, 267. Starch as food, 268. Industrial uses, 268. 
Table VII; Starch content of crops, 269. Experiment 
Study XXXIV; Starch, 270. Dextrin, Glycogen, Inulin, 
Mannan, Galactan, 270. Pentosans, 272. Experiment 
Study XXXV; Pentosans, 273. Sugars, 274. Sucrose, 274. 
Maltose, 275. Monosaccharoses, 275. Table VIII; Sugar 
content of crops, 276. 

Chapter XVI. Occurrence and Uses of Important Con- 
stituents est Agricultural Plants {Continued) . . 277-287 

Fats and waxes, 277. Plant fats as food, 277. Occur- 
rence, 277. Oil-yielding plants, 278. Table IX; Fat con- 
tent of crops, 280. Lecithin and phytosterol, 280. Phytos- 
terol and cholesterol, 280. Lecithin, 282. Physiological 
function, 283. Proteins, 283. Forms of protein, 283. Oc- 
currence, 284. Table X; Protein content of crops, 285. 
Amino-acids, Alkaloids, Essential Oils, Terpenes, Tannins, 
etc., 286. End products of metabolism, 286. 

Chapter XVII. Animal Foods and Feeding . . . 288-305 

Food value, 288. Quantitative relation of food to energy, 
288. Digestibility, 289. Coefficient of digestibility, 289. 
Table XI; Coefficients of digestibility, 290. Applica- 
tion of coefficients of digestibility, 291. Table XII; 
Digestibility of foods, 292. Energy value of food constitu- 
ents, 293. Fuel value, 293. Bomb calorimeter, 293. 
Calorie, 294. Fuel values in calories, 294. Corrected fuel 
values, 295. Metabolizable or available energy, 295. Table 
XIII; Fuel values of food constituents, 296. Fuel values 
for cattle, 296. Table XIV ; Fuel values and metabolizable 
energy for cattle, 298. Food requirement, 298. Energy 
requirement, 298. Maintenance requirement, 298. Respira- 



TABLE OF CONTENTS XVli 



tion calorimeter, 299. Production value, 299. Energy re- 
quirement for man, 300. Table XV; Production values 
for cattle, 301. Summary, 301. Table XVI; Digestibility 
and energy values for cattle, 302. Nutritive ratio, 302. 
Protein requirement, 303. References to Section III, 305. 



INTRODUCTION 

That part of Agricultural Chemistry which we may term 
Organic has to do with living plants and animals. Considered 
agriculturally as farm products, animals and plants have three 
general uses : (i) as servants of man in performing work, (2) as 
food for animals including man, (3) as material, or for furnish- 
ing material for the use of man in other ways than as food. A 
knowledge of the chemistry of plants and animals is of value 
in understanding their uses in these various ways and in showing 
how their economic value may be increased by greater produc- 
tion, greater conservation or the development of new uses. 

The chemistry of living organisms is termed bio-chemistry 
and as a whole includes all of their physico-chemical relation- 
ships, especially those connected with the inorganic soil food of 
plants. This latter part of bio-chemistry we shall not consider, 
as it belongs to the inorganic division of agricultural chemistry. 

The present study will treat of the composition of plants and 
animals and later of the physiological processes by which their 
body substance is built up and the energy of their living pro- 
cesses is produced. It will thus be largely physiological, with 
especial attention to the general subjects of food and nutrition 
and photosynthesis. 

In order to understand the composition of plants and animals 
and the chemical reactions involved in their living processes, it 
is necessary to know the nature of the individual compounds of 
which they are constituted. As the greater part of these are 
what we term organic, and as these alone are related directly 
to the energy of the living organism, we shall take up first a 
brief study of systematic organic chemistry, discussing only such 
compounds as are directly related to agriculture. 

We shall then be in a position to study the fundamental 
processes and reactions of living things and those particular 
physiological processes which differentiate plants from animals. 



2 INTRODUCTION 

Finally, as the agricultural problems with animals are largely 
those connected with animal feeding and as plants are the main 
food supply of domestic animals, we shall consider the distribu- 
tion of food constituents in plants and the fundamental principles 
of animal foods and feeding together with the use of certain 
plants or plant products for other purposes than feeding, such 
as the manufacture of various materials of economic value. 

Our entire study will thus be divided into three sections, as 
follows : 

Section I. Systematic. The study of the composition, con- 
stitution, character and relationship of the more important 
organic compounds occurring in plants and animals. 

Section II. Physiological. The study of the chemical reac- 
tions involved in the fundamental processes of living organisms, 
in the utilization of food by animals and in photosynthesis in 
plants. 

Section III. Crops, Foods and Feeding. The study of the 
distribution of food constituents in agricultural crops and the 
principles of animal foods and feeding. 



SECTION I 
SYSTEMATIC 

THE CHEMISTRY OF THE MORE IMPORTANT ORGANIC 
COMPOUNDS FOUND IN PLANTS AND ANIMALS 



CHAPTER I 
HYDROCARBONS 

A systematic study of organic chemistry directly connected 
with agriculture should embrace the study of those organic 
compounds which are of primary importance either as con- 
stituents of plants and animals or as products formed from them 
either naturally or artificially. In order to understand these 
compounds in their character and their relation to each other, 
it will be necessary to consider also a few typical ones which 
are not directly connected with plants or animals in any gen- 
eral agricultural sense. 

Organic chemistry was originally so termed because the 
compounds included in it were produced by living organisms 
(plants and animals). With the development of this branch 
of the science of chemistry, many compounds have become 
known which are truly organic in their character and relation- 
ships, but have never been associated with either plants or 
animals; that is, they are still solely laboratory products. 
This has destroyed the original significance of the term organic. 
The word is still used, however, but in a broader sense. 

All compounds which we class as organic are compounds of 
carbon, but a few carbon compounds are still held as truly 
inorganic, so that to term organic chemistry the chemistry of 
the compounds of carbon is not strictly true. However, all 
organic compounds are derivatives of certain fundamental 
compounds of carbon and hydrogen so that the best definition of 
organic chemistry is: the chemistry of the hydrogen com- 
pounds of carbon and their derivatives. 

The hydrogen compounds of carbon will then be the start- 

5 



6 ORGANIC AGRICULTURAL CHEMISTRY 

ing point for the development of our study. As these com- 
pounds consist of the two elements, hydrogen and carbon, they 
are known as hydro-carbons. The hydrocarbons themselves 
are not found in either plants or animals. A few compounds 
of hydrogen and carbon do occur as plant constituents, e.g. 
turpentine, but these do not belong to the primary group of 
hydrocarbons. 

The hydrocarbons are, however, a product of the decom- 
position of plant or animal substances. Plant and animal 
bodies consist largely of complex compounds of the elements 
carbon, hydrogen, oxygen, nitrogen, and sometimes sulphur 
and phosphorus. These compounds on decomposing, either 
by slow natural processes, as have taken place geologically in 
the formation of coal and petroleum, or by rapid artificial pro- 
cesses as in the distillation of wood, break down and yield 
eventually much more simple compounds. In the artificial dis- 
tillation, some of the compounds obtained, e.g. wood alcohol 
and acetic acid, still contain carbon, hydrogen and oxygen, 
while others are gases containing carbon and hydrogen only, 
part of the oxygen going off in the form of water (H2O). The 
nitrogen is volatilized in the form of ammonia or ammonia-like 
compounds containing also carbon and hydrogen. In the nat- 
ural geological decomposition of plant and animal substances 
the greater part of the carbon and hydrogen, however, remains 
in coal and petroleum and is easily volatilized from them, in 
the form of compounds containing only these two elements. 
Therefore we may say that petroleum, natural gas, coal and the 
gases formed by the natural decomposition of plant remains 
{marsh gas) , all contain, or at least yield by distillation, products 
which contain true hydrocarbons. 

Although there are different theories as to the origin of such 
substances as petroleum, we may consider it as probably true 
that some at least of the petroleum and other materials, which 
are the sources of hydrocarbons, have been produced by the 
decomposition of plant and animal bodies from which the 
carbon and hydrogen have been derived. 



HYDROCARBONS 7 

EXPERIMENT STUDY I 
Hydrocarbons from Wood and Coal 

(1) (a) Place a few dry wood shavings in a hard glass test 
tube. Fit the test tube with cork, glass and rubber tubing connec- 
tions with a glass jet at the end. Heat the tube slowly and notice 
the moisture given off before the wood begins to char in case the 
wood was not perfectly dry. As the temperature becomes high 
enough to char the wood, notice the collection of moisture on the cool 
parts of the tube. This moisture comes from the decomposed wood. 
What two elements are, therefore, present in the wood? (&) When 
gas is being generated fast enough ignite it at the jet. Note char- 
acter of flame, (c) Hold the burning jet inside a cool, dry, empty 
bottle. Let the jet burn in the bottle as long as possible. What 
does the moisture here prove? After the flame ceases to burn in 
the bottle pour into the bottle 25 c.c. limewater, and shake. The 
white precipitate proves that carbon dioxide (C0 2 ) is present. What 
does this mean? (d) Hold the burning jet against a cold piece of 
porcelain. What does this show? What do all these tests prove 
as to the elements contained in wood ? 

(2) Repeat (1), using powdered soft coal instead of wood. 
The gas produced here is crude illuminating coal gas. 

(3) Mix in a mortar 1 gram of wheat flour and an equal volume 
of fine soda lime. Heat the mixture in a test tube, and hold a piece 
of moist, red litmus paper at the mouth of the tube. Smell the gas 
given off. What is it ? What element does this prove to be present 
in the flour? 

MARSH GAS — METHANE 

Occurrence. — The gas rising from stagnant pools of water 
which contain decaying organic substances, commonly known 
as marsh gas, is known chemically as methane. It has also been 
obtained from petroleum and from coal and is found naturally 
in pockets and crevices in coal strata. It is prepared in the 
laboratory from a salt of acetic acid, a related compound, but 
it will not be necessary at this time to give the reactions in- 
volved in the preparation. (See Exp. II, 1, a.) 



8 ORGANIC AGRICULTURAL CHEMISTRY 

Properties. — By analysis the composition of methane has 
been shown to be 12 parts by mass of carbon to 4 parts by 
mass of hydrogen. Its molecular mass equals 16. It is repre- 
sented, therefore, by the chemical formula CH 4 , or one atom 
of carbon to four atoms of hydrogen. It is a colorless gas 
lighter than air. It burns in the air with a yellow flame which 
deposits carbon on a cold surface. Mixed with air or with 
oxygen in the proportion of one volume of methane to two 
volumes of oxygen it explodes on ignition. Such an explosive 
mixture in coal mines is known as fire damp and is the cause 
of mine explosions. 

Constitution. — It will not be necessary to consider in each 
case the proofs or reasons for conceptions which we shall bring 
forth, but merely state them, assuming that the proofs not here 
given have been fully developed. 

In considering methane as a chemical compound three facts 
are at the foundation of our conceptions in regard to it, and 
these conceptions will lead to an understanding of the definite 
relationship between all of the organic compounds which we 
shall study. These three facts are as follows : 

Methane, CH 4 , is (1) A saturated compound. 

(2) A symmetrical compound, in which all 
four of the hydrogen atoms stand in exactly the same relation 
to the carbon atom. 

(3) The carbon atom in methane and in 
practically all organic compounds is tetravalent, i.e. it has the 
power of holding four and only four hydrogen atoms, or any 
other univalent element, or group of elements, in combination. 

Structural Formula. — The result of these facts is expressed 
in what is termed the structural or constitutional formula for 
methane, i.e. a formula which indicates the way in which the 
compound is built up or constituted. The geometrical figure 
which can represent perfect symmetry of one body joined to 
four others is the regular tetrahedron, and in all space relation 
formulas carbon is considered as being at the center of such a 



HYDROCARBONS 9 

tetrahedron with one hydrogen (in the case of methane) situated 
at each apex. 



Methane 




Such a formula was suggested by van't Hofi" and is, because of 
the wonderful way in which it explains and agrees with facts, 
universally accepted as the complete structural or stereo- 
chemical (space relation) formula for methane. For the sake 
of expression on a plane surface in writing, this formula is 
modified to show only two dimensions, but retaining the ideas 
of symmetry, tetravalence and saturation : 

H 
I 

H — C — H Methane 

I 

H 

This formula is the plane structural formula to represent 
methane and to indicate the three facts previously mentioned : 
(1) saturation of carbon, (2) symmetry of the compound, i.e. 
all the hydrogen atoms are alike in relation to the carbon, and 
(3) tetravalence of carbon. 

EXPERIMENT STUDY II 

Methane, Marsh Gas 

(1) (a) Mix in a mortar 10 grams fused, dry sodium acetate and 
20 grams fine soda lime. Fill a test tube (hard glass) about half full, 
and hold horizontally and tap until the contents lie in the tube leav- 
ing a space along the top. Incline the tube slightly downward when 
heating. Connect the tube by means of glass and rubber tubing so 
as to generate gas and collect over water in small bottles or test 



IO ORGANIC AGRICULTURAL CHEMISTRY 

tubes. Heat the tube slowly and thoroughly until all the gas is 
evolved. Collect three or four bottles or tubes of gas. (b) While 
the gas is generating freely insert a glass jet at the end and ignite 
the gas, and repeat Experiment I, i, b. c. d. 

(2) (a) Bring a flame to the mouth of one of the bottles of gas. 

(b) Mix one bottle with an equal volume of air and ignite the mixture. 

(c) Mix one volume of gas with ten volumes of air and ignite. 

(d) Mix one volume of dry gas with two volumes of dry chlorine gas 
and ignite. Note character of flame and residue of carbon in the 
bottle after ignition. After ignition add a little water to the bottle 
and shake. Test water in bottle for hydrochloric acid, (e) Mix one 
volume of dry gas with two and one half volumes of dry chlorine gas. 
Allow the mixture to stand in the light for several days. Test for 
hydrochloric acid and examine for carbon residue. (Note. — These 
last two experiments are better performed in the lecture room. If 
they have been done there omit, but write up the results in the note- 
book.) 

SUBSTITUTION 

For the most part the hydrocarbons are characterized as 
inactive compounds. This is indicated by the name given to 
those similar to methane, viz. paraffins, from " parum af- 
finitas" little affinity. This property of inactivity shows itself 
toward almost all ordinary reagents, such as acids, alkalies, 
oxidizing and reducing agents, etc. Toward only one group 
of elements does methane show any reactivity. The halogen 
elements, chlorine and bromine, do react with methane when 
brought in contact with it. 

When chlorine reacts with methane suddenly at high tem- 
peratures, as when a mixture of the two gases is ignited, the 
methane is decomposed and all of the hydrogen unites with the 
chlorine, forming hydrogen chloride, and the carbon is left free. 
(See Exp. II, 2, d~) This is represented by the following re- 
action : 

CH 4 + 2C1 2 ->C+4HC1 

Methane 

If, however, the action takes place slowly, as in case a mixture 
of the two gases is allowed to stand in diffused light, then 



HYDROCARBONS II 

another reaction takes place by which the four hydrogen atoms 
are removed by the chlorine atom by atom, and each time a 
hydrogen atom is removed a chlorine atom takes its place. 
(See Exp. II, 2, e.) The steps in this series of reactions are as 
follows : 

4 CH 4 +4 Cl 2 -> 4 CH3CI + 4 HC1 

Methane 

3 CH3CI + 3 Cla -> 3 CH 2 C1 2 + 3 HC1 
2 CH 2 C1 2 + 2 Cla -> 2 CHCI3 + 2 HC1 
CHCI3 + Cl2-> CCI4 + HC1 
or 4 CH4+ioC1 2 ->(CH 3 C1+CH 2 C1 2 +CHC13+CC1 4 ) + ioHC1 

Methane 

Such products formed from the hydrocarbons or other com- 
pounds by substituting for one or more of the hydrogen atoms 
an equivalent number of atoms of other elements are known 
as substitution products, and the phenomenon is called substitu- 
tion. We shall find that numerous series of substitution prod- 
ucts are known which have different groups acting as substitutes. 
The most important ones are those in which one of the halogen 
elements (CI, Br, I), the hydroxyl group (OH), the amino group 
(NH 2 ), the nitro group (N0 2 ), the sulphuric acid group (S0 2 OH), 
the cyanogen group (CN) become substituted for a hydrogen 
atom of a hydrocarbon. Also one oxygen atom (O) may take 
the place of two hydrogen atoms. 

Of the substitution products just described as obtained from 
methane by the action of chlorine two are well-known sub- 
stances, viz. CHCI3, chloroform, and CC1 4 , carbon tetrachloride. 
Collectively they are known as the chlor -methanes and they are 
distinguished by prefixes denoting the number of chlorine 
atoms substituted. The condensed structural formulas and 
also the full structural formulas together with the names are 
shown as follows : 

H 

I 
CH3CI — Mono-chlor-methane, H - C - CI 

I 
H 



12 ORGANIC AGRICULTURAL CHEMISTRY 

H 

I 
CH2CI2 — Di-chlor-methane, H - C - CI 

I 
CI 

CI 

I 
CHCI3 — Tri-chlor-methane, H - C - CI 

I 
CI 

CI 

I 
CCI4 — Tetra-chlor-methane, CI - C - CI 

I 
CI 

In these compounds and similar ones the groups (CH 3 ), (CH 2 ), 
(CH) or others containing several carbon groups, which will 
be found running unchanged through a series of related com- 
pounds, are termed radicals. The radical CH 3 is called methyl 
and CH3CI is known as methyl chloride as well as mono-chlor- 
methane. 

By reactions which we shall not now discuss there have been 
produced other mono substitution products of methane in which 
the hydroxyl, amino, nitro, cyanogen, etc., groups have been 
substituted for a hydrogen and they are known by analogous 
names. The relationship between them and methane itself 
may be grasped by considering them together. 

CH 3 - H, Methyl hydride (Methane) 

CH 3 — CI, Methyl chloride (Mono-chlor-methane) 

CH 3 — Br, Methyl bromide (Mono-brom-methane) 

CH 3 — I, Methyl iodide (Mono-iodo-methane) 

CH 3 — OH, Methyl hydroxide (Mono-hydroxy-methane) 

CH 3 — NH 2 , Methyl amine (Mono-amino-methane) 

CH 3 — CN, Methyl cyanide (Mono-cyano-methane) 

The group of substitution products of methane in which one 
halogen element is substituted for a hydrogen atom is known by 



HYDROCARBONS 13 

the name of mono-halogen methanes or methyl halides. The 
reactions of these methyl halides lead to conceptions in regard 
to the structure and relationship of other hydrocarbons and 
other substitution products. 

SYNTHESIS OF HIGHER HYDROCARBONS 

Methane, CH 4 , is the simplest of a long series of similar com- 
pounds which increase gradually both in carbon and hydrogen 
content. The first six members of this series together with a 
few of the highest may be given as an illustration. 

Methane or Paraffin Series of Hydrocarbons, C n H2„ + 2. 



CH 4 , 


Methane 


CeHi 4 , 


Hexane 


C2H6, 


Ethane 


C7H16, 


Heptane 


C3H8, 


Propane 


C10H22, 


Decane 


C4H10, Butane 


C20H42, 


Eicosane 


C5H12; 


, Pentane 


C60H122 


, Hexacontane 



Above the fourth member the prefix of the name denotes the 
number of carbon atoms in the compound. It will be seen that 
the successive compounds differ in composition by one carbon 
and two hydrogens, i.e. by CH 2 , and that for the whole series 
the general formula, C„H 2rt + 2 , holds. 

What are these compounds as to structure and constitution? 
When methyl iodide, CH 3 I, is treated with sodium, ethane is 
formed and the iodine unites with the sodium, forming sodium 
iodide. The reaction takes place in the proportion of two 
molecules of methyl iodide to one molecule (two atoms) of 
sodium and yields one molecule of ethane and two molecules of 
sodium iodide as follows : 

CH 3 - (I+Na- Na+ 1) - CH 3 -> CH 3 - CHs + 2 Nal 

Methyl iodide Ethane 

This reaction means that ethane, C 2 H 6 , must be considered 
as composed of two methyl radicals joined together, viz. 
CH 3 — CH 3 . Using the complete structural formulas, we write 
the reaction : 



14 ORGANIC AGRICULTURAL CHEMISTRY 

N H H H 

I III 

H-C-(I+Na-Na+I)-C-H -> H-C-C-H+2 Nal 

I III 

H H H H 

Methyl iodide Ethane 

H H 

I I 
Ethane, C 2 H 6 , is therefore CH3-CH3, or H-C-C-H 

H H 

The monohalogen ethanes are exactly analogous to the mono- 
halogen methanes and are, e.g., 



CH3-CH2I or H-C-C-I, Monoiodo-ethane 



H H 

T I 

(ethyl iodide) 



I I 

H H 

In an exactly analogous way propane, C 3 H 8 , may be made 
from ethyl iodide (monoiodo-ethane) and methyl iodide in the 
presence of sodium. 

CH3-CH 2 -(I+Na-Na+I)-CH3-^CH3-CH 2 -CH 3 +2Nai 

Ethyl iodide Methyl iodide Propane 

or 

H H H H H H 

H-C-C-(I+Na-Na+I)-C-H->H-C-C-C-H+ 2 NaI 

II I III 

H H H H H H 

Ethyl iodide Methyl iodide Propane 

By this same general reaction each of the successive hydro- 
carbons may be synthesized, and we find that the structure of 
each is represented by a continually elongated chain of carbon 
groups, the two end carbon groups being CH 3 and all of the in- 
termediate groups CH 2 . Also each hydrocarbon is the methyl 
substitution product of the one preceding it. 



HYDROCARBONS 15 

CH3-H, Methane 

CH 3 - CH 3 , Ethane (Methyl methane) 

CH 3 - CH 2 - CH 3 , Propane (Methyl ethane) 

CH 3 - CH 2 - CH 2 - CH 3 , Butane (Methyl propane) 

CH 3 - CH 2 - CH 2 - CH 2 - CH 3 , Pentane (Methyl butane) 
CH 3 - CH 2 - CH 2 - CH 2 - CH 2 - CH 3 , Hexane (Methyl pentane) 

CH 3 — (CH 2 ) 58 — CH 3 , Hexacontane 

From each one of these hydrocarbons substitution products 
may be formed containing various elements or groups, CI, 
Br, I, (OH), (NH 2 ), (CN), etc. 

ISOMERISM 

When we come to study the substitution products of pro- 
pane we find a new phenomenon. When propane, C 3 H 8 , or 
CH 3 — CH 2 — CH3, is converted into monoiodo-propane or propyl 
iodide, there are formed two compounds of identical composition 
but of distinctly different properties. Such compounds of like 
composition but different properties are known as isomeric 
compounds and the phenomenon is known as isomerism. 
Isomerism we shall find is a most striking and important phe- 
nomenon of organic compounds. 

The explanation of the formation of two propyl iodides is 
derived from our idea of the structure of propane. By examin- 
ing the formula of propane, 

H H H 
I I I 

CH3-CH2-CH3 Or H-C-C-C-H Propane 

I I I 

H H H 

we see that the six hydrogens in the two end carbon groups may 
be considered to be in a different relation, in the compound, to 
the two hydrogens united to the middle carbon. If then one 
hydrogen of each of these two sets is substituted, one at one 
time and the other at another time, by iodine, we can represent 
the resulting compounds by the following structural formulas : 



1 6 ORGANIC AGRICULTURAL CHEMISTRY 

H H H H H H 

III III 

H- C- C- C- 1 and H - C-C- C-HPro Py l iodides 

III III 

H H H H I H 

or CH 3 - CH 2 - CH 2 I and CH 3 - CHI - CH 3 

These two iodine atoms are evidently in different positions in 
the compound, i.e. have different relations to the rest of the 
compound. The fact that two propyl iodide compounds exist 
isomeric with each other indicates that our supposition of the 
difference of the two substituted hydrogen atoms is correct. 

The two isomeric propyl iodides are known as propyl iodide 
and as iso-propyl iodide (isomeric propyl iodide). 

If now by the reaction with sodium a new methyl group is 
placed in the position of the iodine in these two propyl iodides, 
we shall have two hydrocarbons formed each of the composition 
C 4 Hio, and in which a difference in structure exists like that in 
the isomeric propyl iodides, i.e. : 

CH3 — CH2 — CH2I — > CH3 — CH2 — CH2 — CH3 

Propyl iodide Butane 

CH3-CH-CH3 ->CH 3 -CH-CH3 

I I 

I CH 3 

Iso-propyl iodide Iso-butane 

Here also fact and theory agree, for there are known two 
butane hydrocarbons isomeric with each other. Without de- 
veloping the idea further we can gain some conception of the 
meaning of isomerism and the possibility of the existence of 
isomeric compounds both among the hydrocarbons themselves 
and among all the different classes of substitution products. 
Such isomerism, when the difference in the isomeric compounds 
is explained by difference in structure or by difference in the 
position which a substituting element or group takes, is known 
as structural or position isomerism. We shall later have to do 
with a further development of the idea of isomerism when we 
consider the space relationship of the molecule in connection 



HYDROCARBONS 17 

with the tetrahedral formula for methane or for the carbon 
atoms in organic compounds. This new isomerism is known 
as space or stereo isomerism. 

Having thus developed, through a consideration of a few 
compounds, some of the fundamental theoretical conceptions 
of organic chemistry we shall now consider the compounds 
themselves. 

The hydrocarbons are of importance to agriculture as con- 
stituents of products which possess great value because of 
extensive general use, such as gasoline, kerosene, lubricating 
oils and greases, vaseline and paraffin, all of which are obtained 
by the fractional distillation of petroleum. Also illuminating 
gas obtained by distilling coal. They have an indirect value 
also in the theoretical ways just explained, and in the fact that 
they are products of the decomposition of plant and animal 
bodies. An interesting fact is that the lower hydrocarbons, CH 4 , 
methane, C 2 H 6 , ethane, C 3 H8, propane and C 4 Hi , butane, are 
gases, the next few liquids, and the higher members solids. 
The solid members are contained in paraffin and, like it, are 
wax-like substances. 



CHAPTER II 

SUBSTITUTION PRODUCTS OF THE 
HYDROCARBONS 

HALOGEN COMPOUNDS 

Halogen Methanes 

As already explained, the halogen substitution products or 
alkyl halides result from the substitution of one of the halogens 
for an equivalent amount of hydrogen of the hydrocarbon. 
This substitution does not take place directly except in a few 
cases, and methods of preparation usually start with other 
compounds than the hydrocarbons themselves. It is not 
necessary for us to consider these reactions of preparation, as 
they involve the alcohols, which we shall study later, and they 
are not essential to an understanding of the group as a whole 
and the special properties of a few common representatives. 
The chief importance of these compounds is in synthetic re- 
actions. Of the halogen substitution products of methane, 
three are common substances. These are : 

Tri-chlor-methane, chloroform, CHCI3 
Tri-iodo-methane, iodoform, CHI 3 
Tetra-chlor-methane, carbon tetrachloride, CC1 4 

Chloroform is a heavy, colorless liquid possessing a sweet, 
suffocating odor. It is non-inflammable and only slightly 
soluble in water. It is one of the two most common anaesthetics, 
its use as such being discovered in 1848 by Simpson, an English- 
man. It is made from alcohol or from acetone by the action of 
chlorine. 

Iodoform is a yellow, crystalline solid almost insoluble in 

18 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 19 

water and soluble in alcohol. It is a very important disinfectant 
and antiseptic used especially in the dressing of wounds. It also 
is made from alcohol and its formation is a test for the presence 
of alcohol. (See Exp. VII, 4.) 

Carbon Tetrachloride, or tetra-chlor-methane, is a heavy 
liquid resembling chloroform in appearance and general char- 
acter, but is non-anaesthetic. Its chief use is as a solvent for 
fats and oils. It is non-inflammable and is used as a constituent 
of non-inflammable cleaning liquids and also of some fire- ex- 
tinguishing liquids. 

EXPERIMENT STUDY III 
Halogen Substitution Products 

(1) Chloroform, CHC1 3 , Tri-chlor-methane. (a) Using 2 to 3 c.c. 
chloroform, test the compound for general properties, e.g. color, 
odor, inflammability (pour a few drops on a watch glass and apply 
flame), solubility in water, in alcohol, specific gravity (heavier or 
lighter than water), etc. (b) Test solvent action on (1) iodine, (2) fats 
or oils, (3) sulphur. 

(2) Iodoform, CHI 3 , Tri-iodo-methane. Examine iodoform as to 
general character and crystal form (microscope or lens). Test for 
color, odor, and solubility in water and alcohol. 

(3) Carbon Tetrachloride, CC1*, Tetra-chlor-methane. Repeat the 
chloroform tests with carbon tetrachloride. 

Halogen Ethanes 

Mono-halogen Ethanes. — The halogen ethanes or ethyl hal- 
ides are analogous to the halogen methanes, e.g. : 

CH 4 , Methane CH 3 I, Methyl iodide 

C 2 H 6 , Ethane C 2 H 5 I, Ethyl iodide 

C 2 H 5 Br, Ethyl bromide 

C2H5CI, Ethyl chloride 

These mono-halogen ethanes are all known and are important 
synthetic reagents. Ethyl chloride and ethyl bromide are also 
used as anaesthetics. 



20 ORGANIC AGRICULTURAL CHEMISTRY 

Di-halogen Ethanes. — The di-halogen ethanes are significant 
as introducing to our consideration a new type of isomerism. 
Analogous to di-chlor-methane and di-brom-methane, we have 
the corresponding di-halogen ethanes : 

CH2CI2 C2H4CI2 C2H4Br2 

Di-chlor-methane Di-chlor-ethane Di-brom-ethane 

Isomerism of Di-substituted Ethanes. — Not only do we 
know di-brom-ethane, but there are two isomeric compounds 
of this same composition, C 2 H 4 Br 2 . We should mention the 
fact that only one mono-substituted ethane of any kind is 
known, and from this we gain the idea that all six of the hydrogen 
atoms in ethane are alike. When, however, we consider the 
entrance into the ethane molecule of two substituting elements 
in place of two hydrogen atoms, we see at once, from our con- 
stitutional formula of ethane, that two products are possible. 
The fact as already stated is that two are known. By examin- 
ing the formula for ethane, we see that it would be possible to 
substitute two hydrogens united to the same carbon atom or two 
hydrogens one of which is united to one carbon and the other 
united to the second carbon. Expressing this idea by our struc- 
tural formulas we have : 

H H H H H H 

II II II 

H-C-C-H; H-C-C-Br; Br-C-C-Br 

II II II 

H H H Br H H 

Ethane Dz-brom-ethanes 

This, then, explains the existence of two isomeric di-brom- 
ethanes. From the fact that one structure represents a sym- 
metrical compound while the other represents an unsymmetrical 
one, the two compounds are known as symmetrical di-brom- 
ethane and unsymmetrical di-brom-ethane. The symmetrical 
di-brom-ethane is directly related to a new kind of hydrocarbon 
called ethylene (C 2 H 4 ), and the bromide is therefore known 
as ethylene bromide. The unsymmetrical compound is also 
known as ethylidene bromide. We shall mention ethylene again 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 21 

later and show how its relation to symmetrical di-brom-ethane 
leads to ideas in regard to the structure of ethylene. Writing 
the condensed structural formulas for these compounds we 
have: 

CH 3 - CH 3 CH 3 - CHBr 2 CH 2 Br - CH 2 Br 

Ethane Unsymmetrical Symmetrical 

di-brom-ethane di-brom-ethane 

Ethylidene bromide Ethylene bromide 

This isomerism, as illustrated by the two di-brom-ethanes, 
applies to all di-substituted ethanes so that for each class we 
have unsymmetrical or ethylidene and symmetrical or ethylene 
di-substituted ethanes. 



CYANIDES AND AMINES 

Cyanides. — When a halogen substitution product reacts 
with potassium cyanide, KCN, a compound is formed in which 
the halogen is replaced by the group or radical, CN. 

CH 3 (I + K)CN -> CH 3 - CN + KI 

Methyl iodide Methyl cyanide 

This new compound is CH^ — CN and is known as methyl 
cyanide just as CH 3 — I is methyl iodide. This cyanogen 
group may be substituted in practically any position where a 
halogen atom is present and we therefore have a large number 
of cyanide compounds. As we shall find, the simple cyanides 
are directly related to the acids, and on that account are known 
as acid nitrites. 

Among the compounds studied in inorganic chemistry the 
cyanides occupied an important place. The cyanides of iron, 
in particular the double cyanides, are noticeable for their color 
and are important as dyes. The name cyanide comes from a 
Greek word (cyanos) meaning blue. 

Amines. — By an analogous reaction to the one just described, 
ammonia reacts with a halogen substitution product and a 
compound is formed in which the halogen is replaced by the 
group or radical, NH 2 , which is the radical of ammonia. 



22 ORGANIC AGRICULTURAL CHEMISTRY 

CH 3 (I + H)NH 2 -> CH3 - NH 2 + HI 

Methyl iodide Methyl amine 

This new compound is known as amino-methane or methyl 
amine. These names are significant and are exactly analogous 
to those of the halogen substitution products. The group, 
NH2, is known as the amine or amino group, and the general 
name for compounds containing this group is amines or amino 
compounds. Practically in all places in which we may sub- 
stitute halogens we may likewise substitute the amino radical, 
and the amines constitute a large and important group of 
compounds. Several of these compounds which we shall 
consider later are directly connected with animal and vegetable 
life. Some of them are found naturally in herring brine, in 
the distillation products of beet sugar residues, in certain plants 
and in other places. 

The importance of amino compounds in connection with 
agriculture is that in all of their characters they are ammonia 
derivatives. Methyl amine may be looked upon either as a 
derivative of methane or of ammonia. 



H 




1 
H-C-NH 2 




1 


\CH 3 


H 




Amino-methane 


Methyl ammonia (amine) 



In fact it is the ammonia character of these compounds which 
is the striking thing. They are alkaline in reaction, have an 
ammoniacal odor and form salts with acids just as ammonia 
does. In the conversion of ammonia into ammonium salts 
the trivalent nitrogen in ammonia becomes pentavalent in 
the salts as follows: 

/H /OH 

N^-H + HC1 -> N(-H or NH 4 C1 

\h \Nh 

\C1 

Ammonia Ammonium chloride 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 23 

/CHg 
/CH 3 />H 

N^-H + HC1 -> N^-H 

Methyl amine Methyl ammonium chloride 

On decomposition the amines yield their nitrogen as ammonia, 
and it is their ammonia relationship which connects them with 
agriculture. The most complex nitrogen compounds of the 
animal body, the proteins, are unquestionably amino com- 
pounds, and on breaking down they yield simpler amino com- 
pounds, one of these being urea, and these in turn yield the 
nitrogen finally as ammonia, in which form it begins its con- 
nection with plant life as plant food in the soil. These complex 
amino compounds will be considered later. 

Cyan-amide. — One amino compound should now be con- 
sidered in more detail. We have just discussed first the cyanides 
and then the amines. A compound is known in which this 
cyanide radical is substituted in ammonia just as, in methyl 
amine, methyl is substituted in ammonia. 

/H /H /H 

H^-H <- Nf-H -> N^-H or NC - NH 2 
\CH 3 NEE NCN 

Methyl amine Ammonia Cyanamide 

The compound is known as cyan-amide. It forms salts with 
metals such as silver and calcium in which the metal replaces 
an equivalent amount of hydrogen of the amino group. 

/H /Ag ^Ca 

N^-H N^-Ag N< orNC-N=Ca 

\CN \CN X CN 

Cyanamide Silver Calcium 

cyanamide cyanamide 

Calcium Cyanamide. — This calcium salt or calcium cyana- 
mide is a new and, without doubt, a very important nitrogen 
fertilizer. Its value to plants is due to its ammonia character, 
as the nitrogen in this new compound in which no hydrogen is 



24 ORGANIC AGRICULTURAL CHEMISTRY 

left retains its original ammonia nature. On decomposition 
with water it goes back to ammonia. 

NC - NCa + 4 H 2 -> 2 NH3 + Ca(OH) 2 + C0 2 

Calcium 
cyanamide 

This decomposition takes place in steps which cannot be well 
explained here. The exact character of the reaction, at least 
the extent to which it is completed, probably varies under 
different conditions in the soil. The nature of its action is 
still subject to investigation, but there is no doubt that the 
compound will eventually be one of the important forms of 
nitrogen fertilizers. Its common commercial name is lime- 
nitrogen. Its value and importance is largely in connection 
with its commercial method of preparation. 

When carbon (coal) is heated in an electric furnace with lime, 
CaO, the common substance calcium carbide is produced. 

CaO + 3 C -> CaC 2 + CO 

Calcium 
carbide 

This calcium carbide with water yields the common illuminat- 
ing gas acetylene. When, however, it is heated with atmospheric 
nitrogen calcium cyanamide is formed. 

CaC 2 + N 2 ->NC-NCa + C 

Calcium Calcium 

carbide cyanamide 

The source of the nitrogen, therefore, is the atmosphere, and 
we are converting atmospheric nitrogen into a plant fertilizer. 
The utilization of atmospheric nitrogen for the manufacture of 
agricultural nitrogen fertilizers is the great chemical problem 
in relation to agriculture which chemists have been investigating, 
especially during the last quarter of a century, and this com- 
pound, calcium cyanamide, is one of the three important re- 
sults of this work. 

The more detailed study of this compound, including its prac- 
tical application as a fertilizer, belongs to the study of soils and 
fertilizers and not to our present study. 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 25 

EXPERIMENT STUDY IV 

Cyanides 

Caution. Potassium cyanide is an exceedingly strong POISON. 
Examine potassium cyanide very cautiously for color, odor and solu- 
bility in water. Make a solution of about 1 g. in 10 c.c. water. Take 
10 c.c. silver nitrate and add 1 drop of the cyanide solution. Note 
precipitate. Add a few more drops and note result. 

AgN0 3 + KCN -> AgCN + KN0 3 

insol. 
AgCN + KCN -» AgCN -KCN 
sol. 

Double Cyanides. Examine crystals of potassium ferrocyanide, 
KtFe(CN) 6 , or Fe(CN) 2 . 4 KCN, and of potassium ferricyanide, 
K 3 Fe(CN) 6 , or Fe(CN) 3 . 3 KCN, as to general character and solu- 
bility. Add a few drops of each to some ferrous sulphate, FeS04, 
and to some ferric chloride, FeCl3. 

Calcium Cyanamide, CaN— CN. Examine calcium cyanamide for 
general properties. Add 10 g. to 100 c.c. water in a flask. Boil the 
contents of the flask and pass the steam through glass and rubber 
tubing into a beaker containing water and some red litmus paper. 
What gas is produced after considerable boiling (one half hour)? 
Add hydrochloric acid to residue in flask. Filter and test filtrate for 
calcium by means of ammonia and ammonium oxalate, (NH 4 ) 2 C204. 

HYDROXY SUBSTITUTION PRODUCTS OR ALCOHOLS 

When the monohalogen substitution products of the methane 
hydrocarbons are treated with silver hydroxide, Ag(OH), the 
halogen is replaced by the (OH) group or radical. This group 
is known as hydroxyl and the compound resulting is a hydroxy 
substitution product. 

CH 3 (I + Ag) - OH -> CH 3 - OH + Agl 

Methyl iodide Methyl hydroxide 

When methyl iodide is used the product of the reaction is 
methyl hydroxide. It is, however, a common substance known 



26 ORGANIC AGRICULTURAL CHEMISTRY 

as wood alcohol or methyl alcohol. It is the first or lowest mem- 
ber of a large group of similar compounds to which we give the 
class name of alcohol. All alcohols are characterized by this 
hydroxyl group and are hydroxy substitution products of the 
hydrocarbons. They are an exceedingly important class of 
compounds, and are related to agriculture in that they are 
produced from agricultural products, and because they possess 
properties which make them possible of important uses in 
agriculture. 

The second member of the series, viz., the hydroxy-ethane, 
or ethyl hydroxide, CH 3 — CH 2 — OH, is known chemically as 
ethyl alcohol and commonly as grain alcohol, fermentation alcohol 
or simply as alcohol. The first five members of the alcohol 
series, together with two of the higher members, are as follows : 

Alcohols 

CH3-OH Methyl alcohol (Wood 

alcohol) 

CH 3 - CH 2 - OH Ethyl alcohol (Alcohol) 

CH 3 - CH 2 - CH 2 - OH Propyl alcohol 

CH 3 - CH 2 - CH 2 - CH 2 - OH Butyl alcohol 

CH 3 -CH 2 -CH 2 -CH 2 -CH 2 -OH Amyl alcohol 

Ci 6 H 33 -OH Cetyl alcohol 

C 3 oH 6 i-OH Myricyl alcohol 

We shall now consider the first two common alcohols, and 
one or two of the others, more at length in connection with 
their production from agricultural products and their uses. 

EXPERIMENT STUDY V 

Alcohols, Distillation 

Set up apparatus for distillation consisting of (a) distilling flask, 
(b) stopper and thermometer, (c) condenser, (d) adapter, (e) receiver. 
(See drawing on laboratory blackboard.) 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 27 

(1) Methyl Alcohol, Wood alcohol. In a 250 c.c. flask place 100 c.c. 
of methyl alcohol. Heat the flask gradually until the liquid begins 
to distill over and note the temperature at this instant. Continue 
slowly until about 30 cc. have distilled over. Determine the specific 
gravity of the original alcohol and of the distillate. 

(2) Repeat (1) using ethyl alcohol. 

(3) Repeat (1) using amyl alcohol. 

(4) Fractional Distillation. Measure out 100 c.c. of ethyl alcohol. 
Determine the specific gravity. Add 100 c.c. water and mix 
thoroughly. Determine the specific gravity of the mixture. Place 
the mixture in a 500 cc. distilling flask, heat gradually and distill very 
slowly. Note the temperature at the beginning of the distillation. 
Distill over 30 c.c. and note temperature at this time. Without stop- 
ping the distillation change receiver and collect a second 30 c.c. frac- 
tion, noting temperature as before. In the same way collect a third, 
fourth and fifth fraction, noting temperature carefully at the end of 
each fraction which is also the beginning temperature of the next 
higher fraction. Cease the distillation at the end of the fifth 30 c.c. 
fraction. Determine the specific gravity of each fraction and of the 
residue. Calculate the per cent of alcohol in each fraction and in the 
residue from the table (Table I) and tabulate the results as follows : 



Fractional Distillation of Ethyl Alcohol 



Volume c.c. 



Sp. Gr. 



Per Cent 

Alcohol 

by Volume 



Volume ok 

Pure 

Alcohol 



Original Alcohol . . . 

Water 

Mixture, Alcohol + Water 
Fraction 1, 78 - ° . . 
Fraction 2, ° — ° . . 
Fraction 3, ° — ° . . 
Fraction 4, ° — ° . . 
Fraction 5, ° - ° . . 
Residue, ° — 100 ° . 



100 
100 
200 
30 
30 
30 
30 
30 
? 



0.81 
1. 00 

? 

? 
? 
? 
? 

? 
? 



95-o 
0.0 
? 
? 

? 

? 

? 
? 
? 



95.0 c.c. 
0.0 

? 

? 

? 
? 

? 
? 

? 



What has been effected by this distillation ? If repeated several 
times with each fraction, what would the result be ? 



28 



ORGANIC AGRICULTURAL CHEMISTRY 



TABLE I 

Alcohol 
Alcohol in Per Cent, by Volume Corresponding to Specific Gravities at 



i5-56 c 



I5-56 
Tables, p. 226.) 



of Mixtures of Water and Ethyl Alcohol. (From Landolt's 



dil^_° 


Volume 
Per Cent 


dll^6° 


Volume 
Per Cent 


d 1 ^-- 


Volume 
Per Cent 


15-56° 


Alcohol 


15-56° 


Alcohol 


15-56° 


Alcohol 


1. 000 













0.9985 


1 


O.9592 


35 


0.8900 


70 


0.9970 


2 










0.9956 


3 










0.9942 


4 










0.9928 


5 










0.9915 


6 


O.9519 


40 


0.8773 


75 


0.9902 


7 










0.9890 


8 










0.9878 


9 










0.9866 


10 










0.9854 


n 


0-9435 


45 


0.8639 


80 


0.9843 


12 










0.9832 


13 










0.9821 


14 


0-9343 


5o 


0.8496 


85 


0.9811 


15 










0.9760 


20 


O.9242 


55 


0.8339 
0.8306 
0.8272 
0.8237 


90 
91 
92 

93 


0.9709 


25 


O.9134 


60 


0.8201 
0.8164 
0.8125 
0.8084 
0.8041 


94 
95 
96 
97 
98 


0-9655 


30 


O.9021 


65 


0-7995 
0.7946 


99 
100 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 29 

Methyl Alcohol {Wood Alcohol) 

Methyl alcohol, CH 3 OH, which is hydroxy-methane, is com- 
monly known as wood alcohol because it is produced by the de- 
structive distillation of wood. When wood, better the hard 
woods such as beech or maple, is heated in closed retorts, or in 
compact piles covered with earth, so that no air, or only a small 
amount, has access to it, the wood is not burned but is decom- 
posed by the heat. Such a process is termed destructive distillation. 
As a result of this heating the wood is decomposed into gaseous 
and liquid products and a residue of carbon or charcoal is left. 
The gaseous products contain some ammonia, but mostly mix- 
tures of gaseous hydrocarbons. The liquid distillate contains 
methyl alcohol together with other compounds to be considered 
later, of which acetic acid (vinegar acid) is the most important. 
The crude distillate is acid in character and is known as pyro- 
ligneous acid. It is dark colored because of tarry compounds 
contained in it, most of which separate as an oily layer, and 
can be removed as such. To obtain the methyl alcohol alone 
from this crude acid distillate the latter is neutralized with 
alkali (lime or caustic soda) and redistilled. The neutralization 
converts the acetic acid into a non-volatile salt so that by the 
redistillation the alcohol is separated from this compound. 
By further purification from the other compounds present, and 
by fractional distillation through what is known as a column 
still, methyl alcohol of 95 per cent purity is obtained. Such 
high grade methyl alcohol is known in this country as Columbian 
Spirits. Absolute or 100 per cent methyl alcohol may be ob- 
tained by forming a crystalline compound with calcium chloride ; 
and this, when filtered off and air dried, is decomposed with 
sulphuric acid and distilled. 

Another source of methyl alcohol is the dry residue obtained 
in the manufacture of beet sugar. When the juice of the 
sugar beet is concentrated and then the sugar crystallized out 
as much as possible, a sirupy residue containing considerable 
solid matter remains. This still contains more or less sugar, 



30 ORGANIC AGRICULTURAL CHEMISTRY 

and by fermentation yields ethyl alcohol, as will be presently 
discussed. After fermentation, and the distillation of the 
ethyl alcohol, the dry residue remaining is destructively dis- 
tilled and methyl alcohol is obtained. Another product ob- 
tained, as was referred to recently, is methyl amine, CH3NH2. 

Methyl alcohol is a water-like liquid boiling at 64. 5 C. and 
has a specific gravity of 0.812 at o° C. It burns with a non- 
luminous flame, and is soluble in water in all proportions. It 
has a characteristic, rather disagreeable odor, and is poisonous 
if taken internally. When so taken it generally affects the eyes, 
and people have been known to be made blind by drinking 
methyl alcohol. Its odor and poisonous properties make it 
useful as a denaturant of ordinary alcohol, i.e. to make ordinary 
alcohol unfit for use as a beverage. 

The chief use of methyl alcohol industrially is as a solvent, 
It is a good solvent of many organic substances which are in- 
soluble in water such as shellac, varnish, celluloid, etc. It is 
also used in the preparation of certain dyes. As its cost of 
manufacture is not great and as it is not subject to taxation, 
being unfit for beverage uses, it is much cheaper than ordinary 
alcohol on which a tax has been paid. Until the passage of the 
denatured alcohol law, it was therefore the chief alcohol used 
for industrial purposes. When slowly oxidized, as when its 
vapor mixed with air is passed over heated copper, it yields a 
compound soon to be considered, known as formaldehyde or 
formalin, a common disinfectant. 

EXPERIMENT STUDY VI 

Methyl Alcohol 

(1) Determine (a) color, (b) odor, (c) inflammability (1 cc. on a 
watch glass), and (d) miscibility with water. (2) Test the solvent 
power of methyl alcohol on the following substances and compare it 
with water as a solvent : * (a) sodium chloride, (b) sugar, (c) camphor, 

1 The best way to perform the solubility tests is as follows : With each substance 
take three very small pieces (just a crystal or two or an amount about the size of 
half a pea) and place in three clean, dry test tubes. Then add to one test tube 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 31 

(d) shellac, (e) rosin, (/) chloroform, (g) iodoform, (h) iodine, (i) sul- 
phur, (7) lard or tallow, (k) cottonseed oil. 

Ethyl Alcohol (Common Alcohol) 

Properties. — Ethyl alcohol, CH 3 CH 2 OH or C2H5OH, is the 
common alcohol of commerce, and is contained in a greater or 
less amount in alcoholic beverages. It bears the same relation 
to methyl alcohol that ethane does to methane. It is a water- 
like liquid similar to methyl alcohol in general appearance and 
properties. It boils at 78 and has a specific gravity of 0.806 
at o° C. It differs from methyl alcohol in having a pleasant 
odor. It burns with a non-luminous flame and mixes with 
water in all proportions. It resembles methyl alcohol in its 
solvent properties, but is stronger in this action toward most 
organic substances. It forms crystalline compounds with 
certain salts, e.g. calcium chloride, CaCl 2 . 

In dilute form, as it is found in beverages, alcohol has been 
known from ancient times and in nearly all countries. It was 
first obtained in concentrated pure form in the Middle Ages, 
and absolute or 100 per cent alcohol was made first in 1796, 
and its composition determined in 1808. 

EXPERIMENT STUDY VII 

Ethyl Alcohol 

(1) (2) Perform all of the tests under Experiment VI, 1, 2, with 
ethyl alcohol. (3) To a little absolute ethyl alcohol in a test tube, 
which is fitted to generate gas and collect it over water in another 
tube, add a small piece of metallic sodium the size of half a pea. 
Note generation of gas. The gas is hydrogen, as may be proven by 
testing. Repeat addition of sodium if necessary to collect enough 
gas to test. How does the reaction eompare with that of sodium and 
water? After the reaction is over evaporate the alcohol in a small 

about 2 or 3 c.c. of water ; to the second about the same amount of methyl 
alcohol, and to the third ethyl alcohol. Shake each tube, and notice solubility of 
the substance. If it does not dissolve, warm the tube a little. If it is doubtful 
whether any solution has occurred, filter the clear liquid into a watch glass and let 
it evaporate. A residue will show solubility of the original substance. 



32 ORGANIC AGRICULTURAL CHEMISTRY 

evaporating dish or watch glass. Remember alcohol volatilizes com- 
pletely. What is the residue like? It is known as sodium ethylate 
and has the composition C 2 H 5 ONa. By quantitative determination 
it has been proven that only one hydrogen is replaced by sodium. 
This proves that one hydrogen is combined as in water in the form 
of hydroxy I (—OH). 

(4) Test for ethyl alcohol. Prepare two solutions of ethyl alcohol 
in water approximately 1.0 per cent and 0.1 per cent strength. (95 
per cent alcohol 1.0 c.c. + water 99 c.c. = approximately 1.0 per cent 
alcohol. 1.0 per cent alcohol 10.0 c.c. + water 90 c.c. = approxi- 
mately o. 1 per cent alcohol.) Test each of the solutions as follows : 
— Take 10 c.c. of the dilute alcohol in a test tube. Add two or three 
small crystals of iodine. Add 5.0 c.c. dilute KOH or NaOH. Warm 
the mixture. A yellow crystalline precipitate giving the odor of 
iodoform is proof of the presence of alcohol in the original solution. 
Dilute the 0.1 per cent solution 10 times, and repeat the test. 

(5) Test for water in ethyl alcohol. To 5.0 c.c. of 95 per cent ethyl 
alcohol add about 1 g. of anhydrous copper sulphate. Shake and 
let stand. Note change in the copper sulphate. Anhydrous copper 
sulphate is almost white. When it takes up water it is converted 
into the ordinary copper sulphate which is blue and has 5 H 2 as 
water of crystallization, (CuS0 4 . 5 H 2 0). If in the test the copper 
sulphate remains white, the alcohol has no water, i.e. it is absolute 
alcohol. If water is present even in small proportions, the copper 
sulphate will turn blue. 

Alcoholic Fermentation. — It was early discovered that when 
the juice of grapes and other sweet fruits was allowed to ferment 
it took on a sharp taste and affected the body in a stimulating 
manner. This property was found to be due to the presence of 
alcohol in the fermented liquid. In 1836 Cagniard de la Tour 
and von Schwann showed that the alcohol in such fermentation 
was produced by the action of a living plant organism upon 
sugar solutions. This organism is the common yeast plant, 
Saccharomyces cerevisice. Liebig held the view known as the 
mechanical chemical theory of fermentation according to which 
the action was due to some catalytic substance. The views of 
von Schwann and de la Tour were later thoroughly established 
by the Work of Pasteur, and it became an accepted idea that 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 33 

the life process of the yeast plant was directly connected with 
alcoholic fermentation. Pure yeast is able to ferment only 
certain sugars, the two most common ones being glucose, or 
grape sugar, and fructose, or fruit sugar. In the grape juice both 
glucose and the yeast cells are present, the latter occurring 
naturally on the bloom of the grape. 

Enzymes, Zymase. — The recent work of Buchner has shown 
that the fermentation is due not to the living action of the yeast 
cell but to a substance known as zymase, which is secreted by 
the cell. A number of substances are known which act catalyti- 
cally in producing chemical changes of the same nature, and 
which are termed in general fermentations. Ptyalin, the active 
substance in saliva, which converts starch into sugar; pepsin, 
the active substance in gastric juice converting proteins into 
simpler compounds; and diastase, a constituent of sprouting 
grain which also converts starch into sugar, — are examples of 
these substances. They are known as ferments. Because alco- 
holic fermentation, which is the most common process of this 
nature, was supposed, until Buchner's time, to be due to a living 
cell, these other substances which could be obtained in a more 
or less pure condition were distinguished from the yeast plant 
ferment by the name unorganized ferment and later as enzymes, 
the alcoholic ferment being known as an organized ferment. 

Buchner, however, proved that the living yeast cell could be 
entirely destroyed and an unorganized ferment which he called 
zymase obtained from it which in itself possessed the power of 
fermenting grape sugar. Thus alcoholic fermentation is of the 
same nature as these other fermentations, and is due like them 
to the catalytic action of an unorganized ferment or enzyme. 
Thus both of the old views of Liebig and Pasteur may be con- 
sidered as in a way true. The action, as Liebig claimed, is 
catalytic, i.e. depending upon the mere presence or contact of 
the enzyme, not upon its mass, while the living yeast cell is 
necessary, not directly to the fermentation itself, as Pasteur 
claimed, but to the formation of the enzyme, a chemical sub- 
stance which produces the fermentation. 

D 



34 ORGANIC AGRICULTURAL CHEMISTRY 

The alcoholic fermentation of sugar, then, is due to the action 
of the enzyme zymase which is secreted by the yeast cell. In 
grapes both the sugar and enzyme are present and the juice 
therefore ferments naturally with the formation of alcohol, 
the resulting alcoholic liquid being known as wine. As wine 
has considerable commercial value in itself it is not the source 
from which pure or high percentage alcohol is obtained. 

EXPERIMENT STUDY VIII 

Alcoholic Fermentation 

Place 150 ex. of glucose sirup (Karo Corn Sirup) in a 1000 ex. 
flask with 500 ex. of water. Add 20 ex. of nutritive solution 1 (a 
solution of salts for the nutrition of the yeast plant). Mix about 
I cake of yeast with a little water to make a thin mixture. Add this 
yeast to the sugar solution and place stopper in flask with bent glass 
and rubber connection. Connect the rubber tube with a straight 
glass tube and introduce this glass tube into a graduated cylinder 
containing 50 ex. of limewater, Ca(OH) 2 . Pour about 1 ex. of kero- 
sene upon the surface of the limewater to exclude air. Set the whole 
apparatus on the shelf and let it remain at 25 C. until the next exer- 
cise, examining in the interval if possible. What is the precipitate 
formed in the cylinder ? What gas does this prove to be given off ? 
After the fermentation is over pour off 150 ex. of the clear liquid 
into a 300 ex. distilling flask and distill over 100 ex. Test the 
distillate for alcohol as in VII, 4- What are the two products of 
the yeast fermentation of sugar? Test the specific gravity of the 
distillate and calculate the amount of alcohol present in it. As 
this distillate contains all of the alcohol present in the 150 ex. of the 
fermentation liquid calculate the amount of alcohol present in the 
fermentation liquid. This is the method of determining the alcohol 
content of alcoholic liquors. 

Diastase. — The chemical substance which is the ultimate 
source of industrial alcohol is starch. Recently cellulose has 

1 Pasteur salt solution is made as follows : 

Potassium phosphate, 2.0 parts *| 

Calcium phosphate, 0.2 parts ^ 

Magnesium sulphate, 0.2 parts 

Ammonium tartrate, io.o parts J 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 35 

also been used, as will be referred to later. The material from 
which the starch is obtained is generally one of the cereal grains 
or potatoes. Starch, however, is not acted upon by the enzyme 
zymase, so that it cannot be used directly for the alcoholic 
fermentation. When one of the cereal grains, or in general 
any starch-containing seed, sprouts or begins to grow, there is a 
gradual conversion of the starch present in the grain into sugar. 
This change is brought about by the presence in the germinating 
grain of two other enzymes, viz. diastase and maltase. The 
diastase converts the starch into a sugar, maltose, and maltase 
converts the maltose into glucose. When, therefore, these 
enzymes have acted upon starch, it is converted into a sugar 
upon which the alcoholic enzyme zymase can act. In practice 
the grain, usually corn, rye or barley, is allowed to sprout in a 
warm room (6o°-63°) , ground, and water added, making a thin 
mush or mash. This is next treated with yeast and allowed to 
stand at about 25 . Temperatures above 33 are injurious to 
the enzyme. After the fermentation the mash, or wort as it is 
now called, is either placed in retorts and the alcohol distilled 
off directly or the liquid of the wort is separated by filtration. 
The amount of alcohol present in the liquid of the wort is usually 
about 5 per cent, but in some fermenting liquids as in grape 
juice it may reach as high as 14 per cent. Above this it cannot 
go because a stronger solution of alcohol is destructive to the 
enzyme. The distillation of the fermented liquid takes place 
in a still built in several sections so that the alcoholic vapor 
is continually condensed and redistilled (fractionated). By a 
direct distillation from such an apparatus a solution of alcohol 
is obtained of about 90 per cent. This may contain small 
amounts of higher boiling alcohols, propyl and amyl alcohols. 
The non-volatile substances present in the fermentation liquid, 
the principal ones being glycerol and succinic acid, are left 
behind in the retort. For the still greater purification of the 
alcohol it is first mixed with water, making about a 50 per cent 
solution. This allows the separation of some of the amyl 
alcohols as an oily layer. After separation it is now distilled 



36 ORGANIC AGRICULTURAL CHEMISTRY 

again through a rectifying or column still. This is a tall still 
containing many condensing plates so that the alcohol is still 
more perfectly fractionated. By this second distillation the 
purest and strongest alcohol of commerce is obtained. It is 
about 95 per cent, by weight, and is commercially known as 
Cologne spirits. 

Absolute Alcohol. — For the preparation of absolute or ioo 
per cent alcohol the 95 per cent product is placed over quick- 
lime, CaO, and after standing to allow the lime to remove all 
water the whole mass is heated and alcohol passes over as 100 
per cent. Anhydrous copper sulphate may also be used as a 
dehydrating agent, but this is common only in laboratories and 
not in commercial practice. 

Absolute alcohol, because of its affinity for water, acts as a 
dehydrating agent, and is used to remove the last traces of water 
from some substances, especially animal and plant tissues. It 
can be kept only in bottles well stoppered. 

Alcoholic Beverages. — The use of alcoholic beverages is an 
ancient and very general custom. The natural alcoholic bever- 
ages are the weaker in alcoholic content and are simply the 
undistilled fermentation liquids. They are wine, beer, ale, 
stout and others similar in character, but with different names. 
Wine is the simple fermented grape juice and contains 7 per 
cent to 20 per cent alcohol. Those above 14 per cent are 
termed fortified wines because they have alcohol added to them. 
Beer, ale and stout are fermented liquors obtained by filtering or 
decanting off the fermented liquid made from barley in the 
general manner described in the manufacture of alcohol. These 
are still lower in alcohol content than wine, being between 2 
per cent in pale beers to 5 or 6 per cent in ales and porters. The 
characteristic taste or flavor of wines and the names given to 
them depend upon the variety of grape used, the locality where 
the wine is made, or the particular processes involved in its 
manufacture. The same general facts determine the quality 
and name of the beers and ales. 

When a fermented mash prepared from grain or from fruits 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 37 

is distilled without attempting to secure complete purification 
of the distillate or the highest per cent of alcohol possible, there 
is obtained a strong alcoholic distillate possessing certain 
characteristic properties due to the original material used. 
These liquids constitute the distilled liquors known as whisky, 
brandy, cognac, gin, rum, etc. These liquors are much stronger 
in alcohol than either wine or beer and contain usually from 
35 per cent to 40 per cent alcohol. 

Industrial Uses. — The importance of alcohol is not, how- 
ever, in its use in one of these various forms as a beverage, but 
in its wide application in the arts as a solvent or as a substance 
from which other valuable compounds are made. In some of 
its industrial uses it may be replaced by its methyl homologue, 
but not in all, at least to advantage. In its synthetical uses it, 
of course, cannot be replaced by the other. 

Taxation. — Because of its use in beverages, which are almost 
wholly luxuries, nearly all civilized countries have considered 
alcohol as a proper article for taxation and for government 
control. The tax is also usually high, so that the cost of pure 
alcohol is far above its cost of actual manufacture. Alcoholic 
beverages, and pure alcohol, that are subject to such taxation 
are taxed according to the amount of pure alcohol present. It 
therefore becomes necessary to determine the strength of 
alcoholic liquids and also to have a fixed standard of strength. 
The analysis of such liquids for per cent, of alcohol has had much 
attention paid to it in order to make the methods reliable and 
applicable to every varying condition. The general method is 
to take a definite amount of the liquid, e.g. 100 c.c. (this will 
be smaller the higher the alcohol content of the liquid), dilute 
to a definite volume (150 c.c.) and then distill off about two 
thirds (100 c.c). The distillate contains the entire amount of 
alcohol present in the liquid and, in case necessary precautions 
have been taken, contains only water in addition. Mixtures of 
pure water and alcohol possess a definite specific gravity for 
each variation in concentration (see Table I), so that the deter- 
mination of the specific gravity of the distillate defines the exact 



38 ORGANIC AGRICULTURAL CHEMISTRY 

amount of alcohol present, and if this is the entire amount pres- 
ent in the original liquid, we have an exact determination of 
the factor desired. 

The standard of strength upon which alcohol is taxed is not, 
as might seem natural, ioo per cent or absolute alcohol, but 
something less than this. In this country the standard strength 
is a 50 per cent by volume alcoholic solution or 42.7 per cent by 
weight. This is termed proof spirit, and tax is always made 
according to per cent proof spirit. 

Denatured Alcohol. — Because of the extremely high tax 
(in the United States the tax equals $1.10 per proof gallon) 
and, therefore, the high price of pure alcohol, also the fact that 
methyl alcohol which has no tax cannot always be substituted 
for it, it is of the utmost importance that alcohol which is to 
be used industrially, not as a beverage, should be removed 
from taxation and thus greatly cheapened in price. In order 
to make this possible it is necessary to render the alcohol for 
industrial uses unfit for beverage purposes. Alcohol so treated 
is termed denatured. Germany and England have had laws in 
operation for some time by means of which alcohol to be used 
industrially is freed from taxation, but it was not until 1906 
that the United States had a law of this kind. Alcohol to be 
used industrially is denatured by the addition of some sub- 
stance which does not interfere with its use, but makes it unfit 
for internal consumption. For example, alcohol to be used in 
the manufacture of ether is denatured by the addition of sul- 
phuric acid which is the reagent necessary when the ether is made. 
For ordinary solvent purposes the denaturant is usually methyl 
alcohol, while a little pyridine is often used to give it an offensive 
odor, and sometimes a colored substance to give it a noticeable 
color. The denatured alcohol law has two advantages. It 
cheapens the cost of alcohol so that things made by its use can 
be cheapened. It also makes it possible to manufacture alcohol 
more generally and to use in its manufacture a great many 
starch, sugar or cellulose-containing materials which have 
heretofore been simply waste products of the farm. The sub- 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 39 

stances generally used are fruit, most vegetables, especially 
potatoes, inferior grain, sawdust, etc. The utilization of 
cellulose, the carbohydrate constituent of sawdust and other 
woody material, for the production of alcohol has been recently 
developed and several processes have been patented. The 
general principle of all of them is to first hydrolyze the cellulose 
to glucose sugar, usually by acid hydrolysis, and then to fer- 
ment the glucose to alcohol by means of yeast, as already de- 
scribed. 

The Higher Alcohols 

Amyl Alcohols. — The only alcohols, in addition to the two 
already described, which we shall consider are the amyl alcohols 
which contain five carbon atoms, i.e. C5H11OH. There are 
eight different isomeric amyl alcohols, all of which are fully 
explained by our ideas of structure which will not be discussed 
here but will be taken up again under lactic acid, p. 69. Two 
of these are found in the products of distillation when a fer- 
mented liquor is distilled. They are known together as fer- 
mentation amyl alcohol. These two alcohols with propyl alcohol 
and butyl alcohol, the two preceding members, constitute the 
greater part of what is commonly known as fusel oil and on ac- 
count of which the oil is also called crude amyl alcohol. 

Amyl alcohol as it is ordinarily obtained, which is a mixture 
of at least two of the eight isomers, is a heavy liquid boiling at 
about 130 , sp. gr. about 0.81. It shows a marked difference 
from methyl, ethyl and propyl alcohols in not being soluble in 
water. It is a striking fact that the solubility in water de- 
creases as the amount of carbon in the alcohol increases, and 
at the same time the specific gravity increases and the boiling 
point rises. The lower alcohols are thus water-like volatile 
liquids soluble in water. The intermediate members from 5 
to 10 carbon atoms are heavy liquids, difficultly volatile and 
insoluble in water, while the higher members are solid, wax- 
like compounds, non-volatile and insoluble in water. 



40 ORGANIC AGRICULTURAL CHEMISTRY 

EXPERIMENT STUDY IX 

Amyl Alcohol 

Perform experiments i, a, b, c, d under Experiment Study VI, 
using amyl alcohol. 

Polyhydroxy Alcohols 

In our study of the halogen substitution products we con- 
sidered the products formed by substituting more than one 
element in place of hydrogen. These compounds, e.g. chlo- 
roform, CHCI3, iodoform, CHI 3 , and ethylene bromide, 
CH 2 Br — CH 2 Br, are termed polyhalogen substitution products. 

In considering the alcohols thus far only the monosubsti- 
tution products have been taken up. Exactly analogous to 
the polyhalogen substitution products we have polyhydroxy 
alcohols. The polyhydroxy alcohols are analogous as bases to 
the polyhydroxy bases of the metals, e.g. calcium hydroxide, 
Ca(OH) 2 , aluminium hydroxide, Al(OH) 3 , etc. They are, 
therefore, often termed polyacid alcohols and will be diacid 
alcohols, triacid, tetraacid, etc., depending upon the number 
of hydroxyl groups present. These polyhydroxy compounds 
which act as bases are termed polyacid because they react with 
more than one molecule of univalent acids, i.e. the metal or rad- 
ical in them will replace two, three, four, etc., acid hydrogens. 

Dihydroxy Alcohols. — It is a fact which has been pretty 
well established that when two hydroxyl groups are united to 
one carbon, the result is, in almost all cases, an unstable com- 
pound which loses water, the hydroxyl groups being thus 
broken. 

In agreement with these ideas is the fact that no dihydroxy 
derivative of methane is known and also that the unsymmetri- 
cal dihydroxy ethane, CH 3 - CH(OH) 2 , is unknown, except as 
derivatives. This will be taken up later. 

The simplest dihydroxy alcohol is the symmetrical dihydroxy 
ethane known as glycol, CH 2 OH— CH 2 OH. This compound 
is called glycol, because it has a sweet taste, as indicated by the 



SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 41 

prefix " glyc " and is an alcohol as the termination " ol " sig- 
nifies. It is also termed ethylene glycol because as a sym- 
metrical disubstituted ethane it is related to ethylene (see p. 
132). It is a thick liquid soluble in water. Its application in 
our study is as an introduction to the polyhydroxy alcohols. 
The dihydroxy products of the hydrocarbons above ethane 
will not be mentioned. 

Trihydroxy Alcohols. — The simplest trihydroxy product is 
the symmetrical trihydroxy substitution product of propane : 

CH 3 CH 2 CH 3 -> CH2OH - CHOH - CH 2 OH 

Propane Trihydroxy propane 

Glycerol (Glycerin). — This trihydroxy propane is the well- 
known compound glycerin. Its better name is glycerol, which 
signifies its alcohol character. It is important to remember 
that these compounds are true alcohols in their chemical char- 
acter and also in many of their physical properties, such as 
solubility. Glycerol is a thick, clear liquid, of sweet taste, solu- 
ble in water. The importance of glycerol in agricultural chem- 
istry is in its relation to the fats and oils as we shall explain 
later. 

Higher Polyhydroxy Alcohols. — The higher polyhydroxy 
alcohols are known in the tetra (4), penta (5) and hexa (6) hy- 
droxyl compounds. The tetrahydroxy alcohols are represented 
by erythritol or erythrite, the penta by arabitol or arabite and 
the hexa by dulcitol or dulcite, sorbitol or sorbite and mannitol 
or mannite. The striking fact which has already been referred 
to is that as the number of hydroxyl groups increases the com- 
pounds possess a sweeter taste. Glycol, glycerol, erythritol, 
mannitol, each is sweeter than the one preceding it. We shall 
find when we study the carbohydrates (sugars) that these poly- 
hydroxy alcohols are directly related to them. 



CHAPTER III 
OXIDATION PRODUCTS OF ALCOHOLS 

ALDEHYDES 

Oxidation may be either the addition of oxygen to a com- 
pound or the removal of hydrogen from it. When primary 
alcohols are oxidized, both of these reactions take place suc- 
cessively, and two important classes of compounds are obtained. 

Compounds in the first of these classes are known as alde- 
hydes from the two words al(cohol) dehyd(rogenatutn). 

Formaldehyde 

When methyl alcohol, CH 3 OH, is oxidized, the following is the 
reaction : 

/H /H 

CH 3 - OH or H- C^-H + 0->H- C^=0 + H 2 
X)H 

Methyl alcohol Formic aldehyde 

The resulting compound is formic aldehyde or formaldehyde. 

This reaction probably takes place in two steps. First, the 
oxygen converts one of the hydrogen atoms of the alcohol into 
a hydroxyl group. The compound resulting contains two hy- 
droxyl groups united to one carbon atom and by loss of water 
would yield the aldehyde as follows : 

/H /H /H 

H-C£-H +0-»H-C<-OH-H 2 0->H-C^O 
X)H X)H 

Methyl alcohol Intermediate compound Formaldehyde 

The fact that the oxidation of hydrogen united to carbon 
results in the conversion of the hydrogen into hydroxyl is proven 
by other reactions and is the probable result here. The fact 

42 



OXIDATION PRODUCTS OF ALCOHOLS 43 

also that the intermediate product above is unknown leads to 
the view previously referred to (p. 40) that when two hydroxyl 
groups are united to one carbon an unstable compound is 
formed which loses water, yielding a stable product. 

Formic aldehyde or, as it is better known, formaldehyde is a 
common disinfectant and germicide. It is ordinarily used in 
the form of a 40 per cent water solution under the name of 
formalin. It is used extensively to disinfect after sickness, and 
as a germicide in connection with numerous plant diseases such 
as potato scab, oat smut, etc. It is also used as a food preserv- 
ative and to preserve anatomical or biological specimens. 
One of the most common uses as a food preservative has been 
in preserving milk. Milk so preserved is especially injurious 
to infants and is strictly prohibited by all health and pure food 
regulations. The compound is a gas, and when used as a dis- 
infectant in case of sickness it is generally freshly prepared in 
this form. The formaldehyde gas is usually generated by pour- 
ing ordinary formalin upon potassium permanganate. The 
permanganate acts violently upon the formaldehyde, oxidizing 
part of it while the heat of the reaction volatilizes the greater 
part, which goes off as a gas rapidly penetrating all parts of a 
room. The formalin is also often sprinkled on a hanging sheet, 
when vaporization of the formaldehyde occurs. When methyl 
alcohol is burned with a small amount of air, or when a mixture 
of air and methyl alcohol vapor is passed over heated copper, 
formaldehyde is the result. This principle is used in making 
alcohol lamps which produce formaldehyde. The odor observed 
when a methyl alcohol lamp is blown out is due to formaldehyde. 
It has a sharp, penetrating, suffocating odor. 

The most important fact in regard to formaldehyde, agricul- 
turally considered, is its biological relation to the synthesis of 
carbohydrates in plants from carbon dioxide and water. For- 
maldehyde may be formed from these two simple compounds, 
and we may represent the reaction empirically as follows : 

CO2 + H 2 -> H-CHO + 2 



44 ORGANIC AGRICULTURAL CHEMISTRY 

This will be referred to again when we discuss photo-synthesis 

(P- 239)- 

Acetaldehyde 

Ethyl alcohol similarly oxidized yields acetic aldehyde or 
acetaldehyde. 

/H /H 

CHs-Cf-H +O^CH3-C^O + H 2 
\OH 

Ethyl alcohol Acetaldehyde 

These two aldehydes are known as formic and acetic aldehydes 
because, on further oxidation, with the taking up of oxygen, they 
yield formic acid and acetic acid respectively. 

Aldehyde Reactions 

Addition Compounds. — Some of the reactions of aldehydes 
are important and should be mentioned, as they will be referred 
to later. When acetaldehyde is treated with ammonia or with 
hydrogen cyanide, addition products are formed probably as 

follows : 

/H /H 

CH 3 - C= O + NH 3 -> CH 3 - C^OH 

\NH 2 

Acetaldehyde Aldehyde ammonia 

/H /H 

CH3- C^O + HCN -> CH3- C^-OH 

\CN 

Acetaldehyde Aldehyde hydrogen cyanide 

Oximes. — When aldehydes are treated with hydroxyl amine 
(hydroxyl ammonia), H 2 N— OH, the two amine hydrogens of 
the latter compound unite with the oxygen of the aldehyde, 
forming water, the following reaction taking place : 

/H ya 

CH 8 -C = (O + HON- 0H-> CH 3 - C = N- OH + H 2 

Aldehyde Hydroxyl amine Ald-oxime 

The product is known as an oxime. 



OXIDATION PRODUCTS OF ALCOHOLS 45 

Phenyl Hydrazones. — An exactly analogous reaction takes 
place with a benzene derivative known as phenyl hydrazine 
which has the formula H 2 N— NH— C 6 H 5 . The reaction is : 

CH3-C = (0+H 2 )N-NH-C 6 H 5 -> CH 3 -C=N-NH-C6H 5 +H 2 
Aldehyde Phenyl hydrazine Phenyl hydrazone 

The product is known as a phenyl hydrazone. 

Both of these last reactions are due to the presence in alde- 
hydes of the group - C = O called the carbonyl group. This 
group is characteristic of aldehydes and ketones, the latter being 
very similar to the aldehydes. In aldehydes the carbonyl car- 
bon has one valence satisfied by a carbon radical, the other by 
hydrogen. In ketones both are satisfied by radicals. 

H CH 3 

I I 

CH 3 -C = CH 3 -C = 

Aldehydes Ketones 

(Acetaldehyde) (Acetone) 

This will be sufficient reference to ketones as we shall wish 
simply to understand them as a class. 

The hydrogen cyanide, hydroxyl amine and phenyl hydrazine 
reactions just discussed are of especial importance in connec- 
tion with the study of the carbohydrates and will be referred 
to again when we consider these compounds. 

EXPERIMENT STUDY X 

Aldehydes 

(1) Formaldehyde, (a) Place 5.0 c.c. of methyl alcohol in a large 
test tube. Heat a spiral coil of copper wire red-hot, and without 
cooling drop it carefully into the tube of alcohol. When the flame 
dies out notice the odor of formaldehyde in the tube. 

(b) Observe general properties of formalin, which is a 40 per cent 
water solution of formaldehyde. 

(c) (Do this in a hood.) To about 5.0 g. of potassium perman- 
ganate in a beaker add 5-10 c.c. formalin. Note odor of formalde- 



46 ORGANIC AGRICULTURAL CHEMISTRY 

hyde and rapid evolution as a gas. This is the best method of using 
formaldehyde as a disinfectant. 

(2) Acetaldehyde. Place 5.0 c.c. of ethyl alcohol in a test tube. 
Add a few crystals (3.0 g.) potassium dichromate (K 2 Cr 2 7 ). Mix 
15.0 c.c. water + 5.0 c.c. sulphuric acid (concentrated). Add the 
mixed acid slowly to the alcohol and dichromate. Warm if necessary. 
Note the action and the sweet odor. The odor is due to acetalde- 
hyde. The green color is due to chromium sulphate. Explain. 

ACIDS 

When the oxidation of primary alcohols proceeds to its limit, 
the second stage of the reaction occurs, oxygen is added to the 
aldehyde, and an acid results. From formaldehyde, formic acid 
is obtained, and from acetaldehyde, acetic acid. The composi- 
tion and constitution of these two acids is shown by the follow- 
ing reactions : 

/H /H /OH 

H - Cf-H + O-^H - C = O + (H 2 0) +0->H - C = O 
\OH 

Methyl alcohol Formaldehyde Formic acid 

yH /H /OH 

CH 3 — C^H +0->CH 3 -C = 0-KH 2 0)+0-> CH 3 — C = 
\OH 

Ethyl alcohol Acetaldehyde Acetic acid 

The formulas just given represent the constitution of the alde- 
hydes and acids as proven by experimental evidence. The 
acids, like the alcohols, contain a hydroxyl group (OH), while 
the aldehydes do not, the hydrogen and oxygen being each 
united directly to carbon. The common way of writing the 
formulas is : 

Formaldehyde, H - CHO Formic acid, H - COOH 

Acetaldehyde, CH3-CHO Acetic acid, CH3-COOH 

Any aldehyde, R - CHO Any organic acid, R - COOH 

It is this COOH group, known as the carboxyl group, which is 
characteristic of acids, and it is the hydroxyl group within this 



OXIDATION PRODUCTS OF ALCOHOLS 47 

group that gives to acids their distinctive acid properties. The 
organic acids, like the inorganic, are neutralized by bases form- 
ing salts. In organic acids it is always this hydroxyl hydrogen 
which is replaced by metals in forming salts and also this 
hydroxyl hydrogen which becomes the positive ion (kation) 
when the acid dissociates in water solution. The formation of 
salts by neutralization of an acid by a base may be illustrated 
by the following reactions : 

H- COOH + KOH -> H- COOK + H 2 

Formic acid Potassium formate 

CH3- COOH + NaOH -> CH 3 - COONa + H 2 

Acetic acid Sodium acetate 

R - COOH + MOH -> R - COOM + H 2 

Any acid Any salt 

Acetic acid series. — The monobasic acids derived from the 
hydrocarbons of the paraffin series which are of especial im- 
portance in our study are given below. They are known as the 
acetic acid series and also as fatty acids as explained later. 





Acetic Acid Series 


Boiling Point 


Formic acid 


H-COOH 


ioi° C. 


Acetic acid 


CH3-COOH 


I20° 


Propionic acid 


CH3-CH 2 -COOH 


I40.2 


Butyric acid 


CH 3 - CH 2 - CH 2 - COOH 


162.5° 


Valeric acid 


C4H9-COOH 


186 


Caproic acid 


CbHu-COOH 


205° 


Caprylic acid 


C 7 H 15 -COOH 


236 


Capric acid 


C 9 Hi 9 -COOH 


270 

Melting Point 


Laurie acid 


CnH 23 -COOH 


43-6° 


Myristic acid 


Ci 3 H 27 -COOH 


53-8° 


Palmitic acid 


C15H31-COOH 


62° 


Stearic acid 


Ci 7 H 35 -COOH 


69.2 


Arachidic acid 


Ci 9 H 39 -COOH 


75° 



48 ORGANIC AGRICULTURAL CHEMISTRY 

The same general relations in their physical properties exist 
between the successive members of the acid series as were 
found in the case of the hydrocarbons, alcohols and other 
homologous series. The lower members are liquids easily dis- 
tilled, the intermediate members are heavier, not easily volatile 
liquids, while the higher members are non-volatile solids. The 
lower members are soluble in water; the higher members are 
not soluble in water, but are usually soluble in alcohol. 

Formic Acid 

Formic acid is found free naturally in certain ants, bees and 
nettles. It is a water-like liquid with a very sharp, irritating 
odor. It produces blisters on the skin. In ants and bees it is 
used as a poison in killing their prey. 

EXPERIMENT STUDY XI 

Formic Acid 

Note. — In testing the action of acids on indicators proceed as 
follows: (a) Test the acid with blue litmus paper, (b) To i.o c.c. 
of acid add 10 c.c. water, and then 2 drops of phenolphthalein solution. 
Add KOH or NaOH drop by drop until the color changes. 

(1) Test formic acid for color, odor, action toward litmus and phe- 
nolphthalein. (2) Shake up about 1.0 g. of mercuric oxide with 2 
or 3 c.c. of acid plus an equal volume of water. After 5 minutes 
filter and heat the nitrate in a test tube connected with delivery tube 
which is immersed in another tube containing a little limewater. 
What gas is evolved? What is the residue? The reaction is as 
follows : 

2 H-COOH + HgO -> (H-COO) 2 Hg + H 2 

Formic acid Mercuric formate (soluble) 

2 (H-COO) 2 Hg + heat -> 2 H-COOHg + C0 2 + HC-OOH 

Mercurous formate (insoluble) 

2 H-COOHg + heat -> 2 Hg + C0 2 + H-COOH 

(3) Dilute 2 c.c. formic acid with an equal volume of water. Add a 
few drops of dilute sulphuric acid. Now heat and add, drop by drop, 



OXIDATION PRODUCTS OF ALCOHOLS 49 

a solution of potassium permanganate. What does the loss of color 
of the permanganate show? When formic acid is heated to decom- 
position with dehydrating agents, it breaks up as follows : 

H-(CO)OH->CO +H 2 

In the presence of an oxidizing agent like potassium permanganate 
this decomposition takes place more easily, the CO being oxidized to 
C0 2 . 

Acetic Acid 

Acetic acid in addition to its occurrence in nature in the form 
of esters is produced on a large scale by the oxidizing fermen- 
tation of the alcohol obtained as the result of fermenting fruit 
juices, especially apple juice or cider. When cider ferments, 
due to the action of the enzyme zymase, alcohol is produced. 
This alcohol is then oxidized through the activity of bacterial 
organisms, acetic acid bacteria, which are present naturally in the 
fruit juice, and the product is acetic acid. 

Sugar + Zymase -> Alcohol 4- C0 2 

CH 3 - CH 2 OH + 2 -> CH 3 - COOH + H 2 

Alcohol Atmospheric Acetic acid 

oxygen + 
bacterial action 

Glacial Acetic Acid. — This form of the acid has the same 
relation to ordinary acetic acid that absolute alcohol has to 
ordinary alcohol, i.e. it is 100 per cent pure. It is obtained 
from strong acetic acid by fractional distillation. Pure acetic 
acid crystallizes at 16.7 , and hence its name glacial acetic acid. 
It is a liquid, boiling point 120 , with a sharp odor and irritating 
effect upon the skin similar to formic acid, but not so strong. 
The salts of acetic acid are mostly crystalline compounds, the 
important ones being those of sodium, potassium, ammonium, 
calcium, iron, aluminium, copper and lead. The iron and 
aluminium acetates are used as mordants in dyeing. The 
copper acetate is a constituent of several insecticides (Paris 
green, etc.), and the lead acetates are used in medicine. 

E 



50 ORGANIC AGRICULTURAL CHEMISTRY 

When acetic acid or the sodium salt o' the acid is heated, 
especially in the presence of a base such as lime, Ca(OH) 2 , or 
sodium hydroxide, NaOH, the acid loses carbon dioxide, CO2, 
and methane, the hydrocarbon next lower to ethane from which 
the acetic acid is derived, is formed, as follows : 

CH 3 - COOH -» CH 4 + C0 2 

Acetic acid Methane 

The lime or sodium hydroxide absorbs the carbon dioxide. 
This reaction is a general one for organic acids by which hydro- 
carbons are obtained. The hydrocarbon in each case contains 
one less carbon atom than the acid. This reaction occurs in 
Experiment II in the preparation of methane. 

Vinegar. — Acetic acid produced by the natural fermenta- 
tion process is known as vinegar. As vinegar may be produced 
by the acetic fermentation of any alcoholic liquid, it will possess 
characteristic properties depending upon its source. Naturally 
this process is slow, the cider being allowed to stand for a long 
time with access to the air. Industrially the process is much 
hastened by allowing the weak alcoholic liquid to flow slowly 
over beechwood shavings which are covered with the acetic 
bacteria while the whole is kept at a temperature of about 33 , 
well aerated. These processes all produce a vinegar which con- 
tains from about 4.6 per cent (U.S.) to 8.0 per cent (France) of 
pure acetic acid. 

Wood Vinegar. — Acetic acid of greater strength than this is 
made by the destructive distillation of wood. This process 
was described under the preparation of methyl alcohol (wood 
alcohol). The distillate obtained from the wood and known as 
pyroligneous acid contains about 4 to 8 per cent of pure acetic 
acid. This is separated from the alcohol, acetone and other 
substances present by conversion into its metallic salts (cal- 
cium, sodium) and the distillation of the alcohol, acetone, etc. 
The acid is again set free by treatment of the calcium acetate 
with sulphuric acid and distilling off the acid. In this way 
acid of about 90 per cent is obtained. 



OXIDATION PRODUCTS OF ALCOHOLS 51 



EXPERIMENT STUDY XH 
Acetic Acid and Vinegar 

(1) (a) Cool 5 c.c. of 100 per cent acetic acid in running water to at 
least 1 5 C. Note crystallization, (b) Dilute the acid with equal 
volume of water and cool again. (2) Test the dilute acetic acid for 
color, odor, taste and action toward indicators. (3) To a little sodium 
carbonate on a watch glass add a few drops of dilute acetic acid. 
What causes the effervescence ? (4) Test acetic acid as in (2) and 
(3) Exp. XI. What does this prove as to ease of oxidation of acetic 
acid? (5) Examine the following salts of acetic acid as to general 
character and solubility in water: (a) sodium acetate, (b) lead 
acetate, (c) copper acetate. (6) Examine pyroligneous acid as to 
general character. Test acidity by means of litmus paper. (7) Test 
for acetic acid, or its salts. (See Experiment XV.) (8) Examine 
cider vinegar as to color, odor, taste, acidity. (9) 3 Measure out in 
a pipette 5.0 c.c. vinegar. Dilute to 50 c.c. Add a few drops of 
phenolphthalein. Now add from pipette, carefully, with stirring, 
N/10 NaOH until color changes. Calculate acidity of vinegar. 
1 c.c. N/10 NaOH is equivalent to .006 g. CH3-COOH. 

POLYCARBOXY ACIDS (POLYBASIC ACIDS) 

Primary alcohols on oxidation yield aldehydes and acids. A 
dihydroxy alcohol, therefore, should yield a dicarboxy acid, 
provided both hydroxyl groups are in a ( — CH 2 OH) grouping 
for this only yields the carboxyl group on oxidation. These 
polycarboxy acids possess polyacid properties depending upon 
the number of carboxyl hydrogens present. They are termed 
polybasic because they react with more than one molecule of a 
monoacid base, e.g NaOH. They are analogous to the poly- 
basic inorganic acids, e.g. sulphuric acid, 

/OH /OH 

H2SO4 or 2 S< and phosphoric acid, H3PO4 or OP(-OH 

M)H \OH 

Two dibasic acids are common and more or less widely distrib- 
uted in nature. 



52 ORGANIC AGRICULTURAL CHEMISTRY 

Oxalic Acid 

Oxalic acid occurs free in certain plants such as sorrel and in 
combination as calcium salts in the leaves and roots or tubers 
of others (such as jack-in-the-pulpit, elephant ears, etc.) and in 
animal urine. 

Oxalic acid is the dicarboxy derivative of ethane, correspond- 
ing to acetic acid, the monocarboxy acid derived from ethane. 

CHa - CHs -+ CH 3 - COOH -> COOH - COOH 

Ethane Acetic acid Oxalic acid 

Oxalic acid is, therefore, simply dicarboxyl, and is the simplest 
representative of the polybasic acids. When oxalic acid is 
heated, it reacts as acetic acid does, it loses C0 2 . Acetic acid 
by such loss of CO2 yields methane while by loss of CO2 oxalic 
acid yields formic acid, our simplest monobasic acid. 

CH 3 - COOH ->■ CH 3 - H + C0 2 

Acetic acid Methane 

COOH- COOH -* H- COOH + C0 2 

Oxalic acid Formic acid 

Now formic acid when heated with dehydrating agents yields 
CO + H 2 

H-COOH->H 2 + CO 

Formic acid 

Therefore the decomposition of oxalic acid when similarly 
heated may be represented by the double reaction : 

-CO2 
COOH - COOH -* H - COOH -» CO + H 2 

Oxalic acid Formic acid Carbon monoxide 

Oxalic acid is a poison and it is possible that this action is 
due to decomposition in the body similar to this decomposition 
by heat, thus forming carbon monoxide, which is a poison. 



OXIDATION PRODUCTS OF ALCOHOLS 53 

EXPERIMENT STUDY XIII 

Oxalic Acid (Poison) 

(1) (a) Examine oxalic acid as to its nature and solubility in water. 
(b) Add a little oxalic acid to limewater and note precipitate of cal- 
cium oxalate, (c) Fit up a test tube for generating gas and collect- 
ing over water. Heat 5 g. of oxalic acid and sulphuric acid in the test 
tube and collect two small bottles or tubes of the gas. To one in- 
troduce by means of a bent tube some NaOH. What gas is absorbed ? 
Now remove tube and test remainder with lighted match. What gas 

is proven here ? 

heat 
COOH -COOH -> C0 2 + CO + H 2 

Oxalic acid 

(2) Dissolve a few crystals of oxalic acid in water. To this solution 
of oxalic acid add drop by drop a solution of potassium permanganate, 
KMn0 4 , to which two or three drops of sulphuric acid have been 
added. The loss of color shows that the permanganate is reduced 
by the oxalic acid. The oxalic acid is oxidized, yielding C0 2 + H 2 0. 
Compare with the preceding reaction and with Exp. XI, 3. 

Succinic Acid 

Succinic acid occurs naturally in amber. Derivatives of it 
are important in animal physiology and also as tartaric and 
malic acids. Its formula is 

CH2COOH 

I 
CH2COOH 

It is the symmetrical dicarboxy derivative of butane. 



CHAPTER IV 
DERIVATIVES OF ALCOHOLS AND ACIDS 

ETHERS 

Ethyl Ether. — One derivative of alcohol should be briefly 
mentioned, as it is such an important compound though not 
related to agriculture. This is ordinary ether or ethyl ether. It 
is one of the two most common anaesthetics, chloroform having 
already been mentioned as the other. 

When alcohol is treated with sulphuric acid in a particular 
way, ether is obtained by the loss of one molecule of water from 
two molecules of the alcohol, and its constitution has been 
proven to bear the relation to alcohol that sodium oxide does 
to sodium hydroxide. 

2Na-OH-»Na20 + H 2 

Sodium hydroxide Sodium 

oxide 

2 C 2 H 5 - OH -> (C 2 H 5 ) 2 + H 2 

Alcohol Ether 

(ethyl hydroxide) (ethyl oxide) 

Ether is a very volatile, limpid, clear liquid with suffocating 
odor. It boils at 34.6 C, is very inflammable, and mixtures of 
air and ether vapor are explosive. It is lighter than water 
and does not mix with it. It is a good solvent of fats, oils, 
waxes, resins, chlorophyll and many other plant constituents. 
It has been shown to possess certain stimulating effects upon 
the germination of seeds and the growth of plants. 

Ether is typical of a whole group of compounds known as 
ethers, all of which have the constitution of oxides of hydro- 
carbon radicals with the general formula R 2 0, in which the two 
radicals may be alike or different. None of the other ethers 
needs further mention. 

54 



DERIVATIVES OF ALCOHOLS AND ACIDS 55 

EXPERIMENT STUDY XIV 

ETHER 

Caution. Ether is very inflammable and should be kept away 
from all flames. 

(1) (a) Heat some water in a beaker to about 50 C. Place 10 c.c. 
of ether in a test tube, and hold the thermometer in the tube with 
the bulb just touching the ether. Place the test tube in the warm 
water until the ether boils. Note temperature. B. P. = 34.6 C. 
(b) Pour about 1 c.c. of ether upon the hand. Note the effect. 
Explain, (c) Pour not over 1 c.c. of ether into a watch glass. Bring 
flame to the ether. Note ease of ignition. 

(2) Observe the general character of ether and test solvent power 
upon (a) sodium chloride, (b) sugar, (c) shellac, (d) lard, (e) cotton- 
seed oil. 

(3) Make the following mixtures : (a) water 5.0 c.c. + ether 5.0 
c.c. (b) Alcohol 5.0 c.c. + ether 5.0 c.c. To (b) add 5.0 c.c. water 
and explain result. 

ACID CHLORIDES AND ACID AMIDES 

These two groups of acid derivatives need be only briefly 
mentioned. When an acid is treated with phosphorus penta- 
chloride, PCIb, or with the tri-chloride, PCI3, the hydroxyl group 
of the acid is replaced by chlorine and a compound known as an 
acid chloride is obtained. The reaction is : 

CH 3 - COOH + PC1 5 -> CH 3 - COC1 + POCI3 + HC1 

Acetic acid Acetyl chloride 

(an acid chloride) 

When an acid chloride is treated with ammonia, the chlorine 
is replaced by the amine group and an acid amide results : 

CH3-COCI + NH 3 -> CH 3 -CONH 2 + HC1 

Acetyl chloride Acet-amide 

The acid amides differ from the amines in that in the latter 
the amine group has been substituted for a hydrogen atom of a 
hydrocarbon while in the former the amine group replaces a 
hydroxyl group of an acid carboxyl. 

R-NH 2 R-CONH2 

Amine Acid amide 



56 ORGANIC AGRICULTURAL CHEMISTRY 

ESTERS OR ETHEREAL SALTS 

Simple Esters 

The acids, with the exception of formic acid, do not usually 
occur free in nature, but are present in combination as a par- 
ticular kind of salt known as an ester or ethereal salt. When an 
acid is neutralized by a base, a salt is formed by the hydroxyl 
hydrogen of the acid being replaced by the metal of the base, 
as follows : 

CH 3 - COO(H + HO)K -> CH3 - COOK + H 2 

Acetic acid Potassium acetate 

Now alcohols, which in general are neutral substances, when 
brought in contact with acids act like bases and neutralize the 
acid. The hydroxyl hydrogen of the acid is replaced by the 
radical of the alcohol and the resulting compound is termed an 
ester or ethereal salt. 

CH 3 - COO(H + HO)C 2 H 5 -> CH 3 - COOC2H5 + H 2 

Acetic acid Ethyl Ethyl acetate 

alcohol 

These esters are exactly analogous to the metallic salts, the 
organic radical taking the place of the metal. They are named 
like the metallic salts, viz. the radical name joined to that of 
the acid with the termination ic changed to ate. Ethyl ace- 
tate is the ethereal salt of the ethyl radical and acetic acid 
made by neutralizing acetic acid with ethyl alcohol. Similarly 
methyl formate is the methyl salt of formic acid, amyl valerate 
is the amyl salt of valeric acid, etc. The importance of esters is 
in the fact that they occur very widely distributed in nature in 
plants, fruits and flowers, and as oils, fats and waxes. Esters 
of the lower acids and lower alcohols are pleasant-smelling, 
volatile liquids (hence the name ethereal salts). They are not 
usually miscible with water, though often slightly soluble in it. 
The higher members are crystalline solids. 

Fruit Flavors. — While it is probably a fact that the odor of 
fruits is due to the presence of esters, it is not fully established, 



DERIVATIVES OF ALCOHOLS AND ACIDS 57 

as they are present in exceedingly small amounts. Esters that 
have been prepared synthetically from some of the middle 
members of the acid and alcohol series do, however, possess the 
odors of certain fruits, and on that account are prepared and 
used as artificial fruit flavors or fruit essences. Some of these 
are as follows : 

Ethyl butyrate, Pineapple essence ; 

Iso-amyl-iso valerate, Apple essence ; 
Amyl butyrate, Apricot essence ; 

Iso-amyl-acetate, Pear essence ; 

etc. 

Fats, Oils and Waxes 

These important plant and animal substances are all true 
esters of alcohols and organic acids. 

Waxes. — The waxes are esters of monohydroxy alcohols, 
similar to ethyl alcohol but containing a larger number of car- 
bon atoms. Beeswax, for example, is composed mostly of the 
ester of myricyl alcohol, C30H61OH, and palmitic acid, 
C15H31COOH, i.e. myricyl palmitate, C15H31COOC30H61. 
Spermaceti, a wax obtained from the head of the sperm whale, 
is mostly the ester of cetyl alcohol, C16H33OH, and palmitic acid, 
i.e. cetyl palmitate, C15H31COOC16H33. 

Fats and Oils. — The fats and oils of vegetable or animal 
origin are true fats and oils as distinguished from numerous 
compounds commonly termed oils, e.g. petroleum oil, oil of 
turpentine, oil of bitter almonds, etc. They are composed of 
mixtures of esters of the trihydroxy alcohol, glycerol and numer- 
ous acids, mostly the monobasic acids of the paraffin series of 
hydrocarbons, which have been given previously. The acids 
which are most common as constituents of fats and oils are, 
butyric, capric, lauric, myristic, palmitic, stearic and arachidic. 
This explains the designation of this series of acids as the fatty 
acids. The names given to these acids indicate their natural 
source in plants or animals : 



58 ORGANIC AGRICULTURAL CHEMISTRY 

Butyric acid in butter, 
Capric acid in goat milk fat, 
Laurie acid in laurel fat, 
Palmitic acid in palm oil, 
Arachidic acid in peanut oil, 
etc. 

Glycerol esters. — Glycerol being a trihydroxy alcohol will 
react with three molecules of a monobasic acid to form an ester. 
An example may be given of the ester formed from butyric 
acid, C 3 H 7 COOH, and glycerol, C 3 H 5 (OH) 3 . 

CH 2 -(OH H)OOC-C 3 H 7 CH 2 -OOC-C 3 H 7 

I I 

CH -(OH + H)OOC-C 3 H 7 ^ CH-OOC-C 3 H 7 + 3 H 2 

I I 

CH 2 -(OH H)OOC-C 3 H 7 CH 2 -OOC-C 3 H 7 

Glycerol 3 Butyric acid Glyceryl tri-butyrate 

(an ester) 

Before considering in further detail the more important vege- 
table and animal fats, we shall discuss the most important re- 
actions connected with them. 

Esterification. — When an alcohol neutralizes an acid, thereby 
forming an ester, the process is termed esterification. 

CH 3 -COO(H+HO)-C 2 H 5 -> CH 3 -COO-C 2 H 5 +H 2 0, esterification 
Acetic acid Ethyl alcohol Ethyl acetate 

In this process water is always lost. This reaction, as written 
above, does not take place in a satisfactory way unless some 
other reagent like sulphuric acid is present to remove the water 
which is the other product of the reaction. If the water is not 
removed, the reaction soon begins to reverse itself, and the ester 
by taking up water is split into the alcohol and acid originally 
used. We express these facts by saying that the reaction is 
reversible and writing it in this way : 

-H 2 0-> 
CH 3 - COO(H + HO) - C 2 H 5 CH 3 - COO - C 2 H 5 

<-H 2 + 



DERIVATIVES OF ALCOHOLS AND ACIDS 59 

The general reaction of esterification or ethereal salt forma- 
tion is one of the best examples we have of reversible reactions. 
By modifying conditions many esterification reactions can be 
made to go in the reverse way. 

On the other hand an ester when boiled with water will take 
up water and be resolved into its constituent acid and alcohol. 
This reaction, like that of esterification, does not proceed to 
completion because as soon as some free acid and alcohol are 
formed they begin to react in the reverse way and re-form the 
ester. If, however, some alkali is present to react with the free 
acid as fast as it is formed, then the decomposition of the ester 
goes on to completion. 

Thus, in esterification, a water absorbing substance must be 
present and in the decomposition of esters alkali must be pres- 
ent. The reaction in both cases is, however, due to water, 
i.e. loss of water in esterification and addition of water in the 
decomposition of the ester. 

-H 2 
CH3-COO-(H+HO)-C 2 H5+(H 2 S0 4 ) -> CH 3 -COO-C 2 H 5 

Esterification 

+ H 2 
CH 3 - COO - QH5 + (KOH) -> CH 3 - COOH + HO - C 2 H 5 

Hydrolysis 

Hydrolysis. — The second reaction, the decomposition of the 
ester, because it involves the addition of water, is termed 
hydrolysis. Hydrolysis and esterification are, therefore, re- 
spective names for the two forms of this reversible reaction. 
We have used as our illustration one of the simple esters, viz. 
ethyl acetate. All esters, however, are subject to these same 
generalizations. 

The esters of glycerol and the fatty acids, i.e. the fats and 
oils, undergo the reaction of hydrolysis when boiled with water 
containing an alkali. When the hydrolysis occurs, the alcohol 
(glycerol) and the acid (butyric, palmitic, stearic, etc.) are 
re-formed. The glycerol remains free, but the acid reacts 



60 ORGANIC AGRICULTURAL CHEMISTRY 

further with the alkali present and the metal salt of the acid is 
formed. 

Soap. — The sodium and potassium salts of some of the 
fatty acids, chiefly palmitic and stearic, form the common 
substance we know as soap. Thus when a fat is boiled with 
dilute alkali, soap and glycerol are the products. 

CH 2 -OOC-C 15 H3i CH 2 -OH KOOC-Q5H31 

CH-OOC-C^ +3 H 2 -> CH-OH + KOOC-C 15 H3i+3 H 2 

I I 

CH 2 -OOC-C 15 H 3 i +3 KOH CH 2 -OH KOOC-C 15 H 31 

Glyceryl-tri-palmitate Saponifica- Glycerol Potassium palmitate 

(fat) tion (soap) 

Saponification. — Such an hydrolysis of a fat is " therefore 
termed an action of saponification or soap formation. The 
saponification of esters is thus a particular form of hydrolysis, 
viz. in the presence of an alkali, and any alkaline hydrolysis 
of an ester is termed saponification even though the product is 
not, strictly speaking, a soap. Its particular importance in 
our study is in connection with the saponification of the animal 
and vegetable fats and oils. Industrially this is in the utiliza- 
tion of fats in the manufacture of soap and glycerol. Physio- 
logically it is in connection with the digestion of fats in the 
animal body which will be considered again in detail when we 
study animal digestion. 

Important Fats and Oils. — Fats differ from oils simply in 
their physical properties, the former being solid at ordinary 
temperature, while the latter are liquid. Chemically they are 
of identical nature, being glycerol esters of the fatty acids, 
differing from the waxes which are esters of monohydroxy 
alcohols and fatty acids. They are not chemical individuals, 
but are mixtures of several, oftentimes many, glycerol esters. 
Individual fats and oils are characterized by the particular 
acids present and by their relative proportions. The identifi- 
cation and analysis of fats and oils is by the determination of 
the physical properties of the fats themselves and of certain 



DERIVATIVES OF ALCOHOLS AND ACIDS 6 1 

chemical constants depending upon the amounts of the different 
acids present. 

Physical Constants. — The esters of the different acids have 
distinctive properties such as melting point, specific gravity, re- 
fractive index, etc. The relative amounts of the different esters 
present give to the fats these definite characters which are 
termed the physical constants. For example, fats containing 
large amounts of palmitic or stearic acid esters are solid at ordi- 
nary temperatures, as in beef fat, mutton tallow, palm oil, etc. 
Those containing large amounts of .the esters of oleic acid, or 
linolic acid, eighteen carbon acids of a new series, are liquids as 
in olive oil, cottonseed oil and linseed oil. Such fats as human 
fat and butter fat lie between these two extremes. 

Chemical Constants. — Oleic acid, linolic acid and linolenic 
acid not only form esters that are liquid but the acids them- 
selves possess distinct chemical properties which they impart 
to the esters. They all belong to series of acids differing from 
the acetic acid series in that while the latter are saturated the 
former are unsaturated. They are related to unsaturated hydro- 
carbons like ethylene, which has been referred to in connection 
with ethylene bromide or symmetrical dibrom ethane. These 
hydrocarbons, acids and fats containing esters of the latter, all 
show their property of unsaturation by readily taking up 
bromine or iodine by addition. The amount of iodine, there- 
fore, which a fat absorbs by addition rests upon the amount of 
the esters of these acids present. This gives us a chemical con- 
stant termed the iodine value by which fats are identified. 

Other chemical constants known as saponification value, 
amount of insoluble acids and amount of volatile acids all depend 
upon the amount of particular groups of acids combined in the 
fat, and are used, together with the iodine value and the physical 
constants already mentioned, for purposes of identification and 
analysis. This brief mention of the basis of analytical methods 
applying to fats and oils is all that is is desirable to make. 

In connection with plant constituents (p. 278) we shall con- 
sider the important vegetable oils as to their occurrence and use. 



62 



ORGANIC AGRICULTURAL CHEMISTRY 



The following table of the more important animal and vege- 
table fats and oils gives their melting points and the esters 
present. 

TABLE II 

Important Fats, Oils and Waxes 





Melting Point or 






Solidifying Point 


Acids of the Principal Esters Present 




Degree C. 




Oils 






Olive . . . 


+ 4° to - 6° 


Oleic, Palmitic, Arachidic, Linolic 


Peanut . . . 


-5° 


Arachidic, Palmitic, Oleic, Linolic 


Cottonseed 


+ i° to + IO° 


Oleic, Palmitic, Linolic 


Maize . . . 


— IO tO — 20 


Palmitic, Stearic, Arachidic, Oleic, Linolic 


Linseed (Flax) 


o * o 
— 20 tO — 27 


Linolic, Linolenic, Palmitic, Oleic 


Castor . . . 


-18 


Stearic, Ricinoleic 


Fats 






Palm . . . 


+ 27° to + 42° 


Palmitic, Oleic 


Cacao-butter . 


+ 30 to + 34° 


Stearic, Palmitic, Oleic, Laurie, Arachidic 


Cocoanut . . 


+ 20° tO + 28° 


Caproic, Capyrlic, Capric, Laurie, Palmitic 


Laurel . . . 


+ 32 to + 36 


Laurie 


Tallow (Beef) 


+ 36 to + 49 


Palmitic, Stearic, Oleic 


Lard .... 


4- 28 to + 45° 


Palmitic, Stearic, Oleic 


Milk Fat 


+ 29 to 4- 35 


Butyric, Caproic, Caprylic, Capric, Myris- 


(Butter) 




tic, Palmitic, Stearic, Oleic 


Human Fat . 





Caprylic, Palmitic, Stearic, Oleic, Butyric, 
Caproic 


Waxes 






Spermaceti 


+ 43 to + 49° 


Palmitic (Cetyl Alcohol Ester) 


Beeswax . . 


+ 62 to 69 


Cerotic, Palmitic (Myricyl Alcohol Esters) 



EXPERIMENT STUDY XV 
Esters or Ethereal Salts 

(1) Esterification. Test for acetic acid or its salts, (a) To 5 c.c. 

of 10 per cent acetic acid add an equal volume of ethyl alcohol. Note 
odor of mixture. Now add about 1 c.c. of sulphuric acid, shake care- 
fully and warm. Note odor now and compare with the odor of the 
mixture of acid and alcohol. The fruity odor is due to the formation 
of the ester ethyl acetate as in the reaction : 



DERIVATIVES OF ALCOHOLS AND ACIDS 63 

CH 3 -COO(H + HO)-C 2 H 5 -> CH 3 -COO-C 2 H 5 +H 2 
Acetic acid Ethyl Ethyl acetate 

alcohol 

The sulphuric acid brings about the loss of the water in the above 
reaction, (b) To a little of any salt of acetic acid, e.g. sodium 
acetate, add a little dilute alcohol and then 1 c.c. of sulphuric acid. 
Warm and note odor of ethyl acetate. The sulphuric acid first 
reacts with the salt of acetic acid, forming free acetic acid. 

CH 3 -COONa + HOS0 2 OH -* CH3-COOH + NaOS0 2 OH 

Sodium acetate Acetic acid 

The free acetic acid then reacts with the alcohol in the presence of 
sulphuric acid and forms the ester. 

(2) Hydrolysis, (a) Place 10 g. ethyl acetate (CH 3 COOC 2 H 5 ), in 
a flask and add 100 c.c. of 10 per cent sodium or potassium hydroxide. 
Connect with a return condenser and boil until no odor of ethyl acetate 
is noticeable. Change the condenser and distill off about 25 c.c. — 50 
c.c. Test the distillate for ethyl alcohol as in Experiment VII, 4. 

(b) Place the remainder of the solution in the flask in an evaporat- 
ing dish. Carefully neutralize excess of alkali with hydrochloric 
acid, avoiding excess of acid by testing with litmus paper. Evapo- 
rate to dryness. Test the dry salt for acetates as in (1), b. The 
reactions involved are : 

CH 3 -COO-C 2 H 5 + KOH -► CH 3 -COOK + C 2 H 5 OH 

Ethyl acetate Potassium Alcohol j 

acetate 

CH3-COOK + H 2 S0 4 -> CH 3 -COOH + KHSO4 

Acetic acid 

CH«-COOH + HO-C2H 5 -> CH 3 -COO-C 2 H 5 

Ethyl acetate 



EXPERIMENT STUDY XVI 

Fats and Soap 

(1) Saponification of a Fat. (a) Use 10 g. of lard, tallow, cotton- 
seed oil or olive oil. Place in an evaporating dish and add 200 c.c. of 
5 per cent NaOH. Heat on water bath until all melted fat has dis- 
appeared. Continue to heat until the liquid has evaporated; or 



64 ORGANIC AGRICULTURAL CHEMISTRY 

without evaporating add about 50 g. of common salt, NaCl, and stir 
thoroughly. The addition of salt causes the soap to separate as a 
solid layer, (b) Test the residue or the separated cake for its soapy 
character, (c) Dissolve some of the soap in water and add sulphuric 
acid until the solution is distinctly acid. The solid separating is the 
free acid originally combined with the glycerol as an ester in the fat. 
The reactions are as follows : 

CH 2 -OOC-C 15 H 3 i CH 2 -OH 

I I 

CH-OOC-Ci 5 H3i + 3 NaOH -> CH-OH + 3 C 15 H 3 i-COONa 

Soap 

CH 2 -OOC-Ci 5 H 31 CH2-OH 

Glyceryl tri-palmitate Glycerol 

(fats) 

C 15 H 31 -COONa + H 2 S0 4 -> Ci 5 H 31 -COOH + NaHS0 4 

Soap Palmitic acid 

(2) Properties of Fats and Soap, (a) Mix 5 c.c. of oil or melted fat 
with an equal volume of water. Shake and then allow to settle. 
Explain, (b) Place two filter papers in two funnels. Keep one per- 
fectly dry and moisten one with water. Pour 10 c.c. of oil or melted 
fat upon each paper. Explain, (c) Mix 5 c.c. of oil with an equal 
volume of soap solution. Shake and allow to stand a few minutes. 
This mixture is called an emulsion. Filter this emulsion through a 
wet filter paper. Explain. 

(3) Hard Water, (a) Place 10 c.c. of limewater, Ca(OH) 2 , in a test 
tube. With a glass tube blow your exhaled breath through the lime- 
water. What is the precipitate which forms? Continue to blow 
through the solution until the precipitate first formed dissolves. 
What compound is now present in solution? Take one-half of this 
solution of calcium acid carbonate and boil thoroughly. Explain. 
Filter or decant off the clear liquid. Boil again to be sure all car- 
bonate has been precipitated. The reactions are as follows : 

Ca(OH) 2 + C0 2 -> CaC0 3 + H 2 

Calcium carbonate (insoluble) 

CaC0 3 + C0 2 + H 2 -> Ca(HC0 3 ) 2 

Calcium acid carbonate (soluble) 

Ca(HC0 3 ) 2 + heat -> CaC0 3 + C0 2 + H 2 



DERIVATIVES OF ALCOHOLS AND ACIDS 65 

(b) Add an equal volume of soap solution to the unboiled acid car- 
bonate solution and to the nitrate from the portion that was boiled. 
Notice the difference. The precipitate formed with the soap and acid 
carbonate solution is the calcium salt of palmitic or other fatty acid. 
Water containing calcium acid carbonate in solution is termed hard. 
This hardness is termed temporary because it is destroyed by boiling 
and precipitating out the calcium, (c) Test solutions of magnesium 
sulphate and calcium sulphate in the same way with soap solution 
without boiling and after boiling. Is there any change in the boiled 
solution? Water containing these salts in solution is termed per- 
manently hard. 



CHAPTER V 
MIXED COMPOUNDS 

We have considered polysubstitution products formed by- 
substituting in a hydrocarbon more than one element or group 
of the same kind. 

Similarly there may be substituted in a hydrocarbon two 
elements or groups, one of one kind and one of another. That 
is, we may have a halogen and hydroxyl, a hydroxyl and car- 
boxyl, an amine group and carboxyl, etc. We shall mention 
only a few of the different known compounds of this general 
class. 

HALOGEN-ALDELHYDES AND HALOGEN-ACIDS 

Halogen-aldehydes 

Tri-chlor-aldehyde. — The mixed halogen and hydroxy com- 
pounds are not important here, but the group represented by 
halogen-aldehydes has an important member. 

When chloroform is prepared from alcohol by the action of 
chlorine, the chlorine first oxidizes the alcohol to aldehyde as 
follows : 

CH3-CH2-OH+Cl2+H 2 0-» CH3-C = +H2O+2HCI 

Ethyl alcohol Acetaldehyde 

The chlorine then acts upon the aldehyde and is substituted 
for all three hydrogen atoms of the methyl group. 

/ H 

CH3-CHO -f 3C1 2 ^CC1 3 -C = + 3HCI 

Acetaldehyde Tri-chlor-aldehyde (chloral) 

66 



MIXED COMPOUNDS 67 

The product is chloral, an oily liquid boiling at 97 C. When 
boiled with alkalies, it breaks down and yields chloroform. It 
possesses the characteristic property of uniting with water, 
forming a crystalline compound known as chloral hydrate 
CCI3— CHO . H 2 0. The evidence seems to point to the con- 
clusion that in chloral hydrate we have a compound of the 
constitution, not of an aldehyde, but of a dihydroxy compound, 
viz. CCI3 - CH(OH) 2 . This is a marked exception to the 
general fact before referred to, that compounds containing two 
hydroxyl groups united to one carbon do not exist. 

Chloral hydrate forms clear monoclinic prisms melting at 
57 C. It is a very valuable and commonly used soporific 
and anaesthetic. 

Halogen-acids 

Chlor-acetic Acids. — As illustrations simply of the halogen- 
acids we may mention the halogen substitution products of 
acetic acid formed by introducing first one, then two, and finally 
three chlorine atoms in acetic acid. 

CH 3 - COOH + CI2 -> CH2CI - COOH + HC1 

Acetic acid Mono-chlor-acetic acid 

CH2CI - COOH + Cl 2 -> CHCI2 - COOH + HC1 

Di-chlor-acetic acid 

CHC1 2 - COOH + Cl 2 -> CCI3 - COOH + HC1 

Tri-chlor-acetic acid 

This reaction takes place with chlorine alone in the direct sun- 
light or by means of iodine tri-chloride, IC1 3 , without sunlight. 
These three compounds have been of the greatest importance 
in establishing our ideas of substitution. All of these substi- 
tuted acetic acids are strongly acid, even more so than acetic 
acid itself. 

HYDROXY-ACIDS 

The polysubstitution products in which both hydroxyl and 
carboxyl groups are present contain some very important com- 
pounds which have direct connection with agriculture. All of 



68 ORGANIC AGRICULTURAL CHEMISTRY 

the mixed compounds are characterized by possessing properties 
distinctive of both classes of compounds represented. The 
hydroxy-acids possess the characteristic properties both of the 
alcohols and the acids. Because alcohols react toward strong 
bases as acids it was at first supposed that these hydroxy-acids 
were dibasic. They are not, however, dibasic unless they at 
the same time contain two carboxyl groups. 

Lactic Acid 

The simplest acid of this group of importance to us is the 
hydroxy-propionic acid, CH 3 - CH(OH) - COOH. It is the 
common acid produced by the souring of milk and known as 
lactic acid. 

By methods of synthesis, which it will not be necessary to 
enter into, lactic acid has been clearly proven to have the con- 
stitution of hydroxy-propionic acid as given above. It is a 
fact, however, that another acid known as hydracrylic acid also 
has the constitution of hydroxy-propionic acid. According to 
our ideas of isomerism the existence of these two isomeric acids 
is readily explained. Two positions are possible in which we 
may substitute the hydroxyl group in propionic acid. 

Propionic acid is CH 3 — CH 2 — COOH and we might obtain 
either 

CH 3 - CH(OH) - COOH or CH 2 (OH) - CH 2 - COOH 

^-hydroxy-propionic acid /3-hydroxy-propionic acid 

These two compounds are distinguished as a-hydroxy-propionic 
acid, in which the hydroxyl group is united to the carbon atom 
next to the carboxyl group, and /^-hydroxy-propionic acid, in 
which the hydroxyl is united to the carbon atom second from 
the carboxyl group. By reactions which leave no doubt it 
has been shown that hydracrylic acid is the /^-compound and 
lactic acid is the ot-compound. 

The /^-hydroxy-propionic acid or hydracrylic acid we need not 
discuss further. Lactic acid, however, possesses properties 
which need further explanation and which bring us to the con- 



MIXED COMPOUNDS 69 

sideration of one of the most striking phenomena of organic 
chemistry. 

Stereo-isomerism or Space-isomerism 

Not only are there known the two structurally isomeric 
hydroxy-propionic acids which are explained as just described, 
but there are also known two other acids which are likewise 
hydroxy-propionic acids and furthermore which are structurally 
identical with lactic acid, i.e. a-hydroxy-propionic acid. 

When milk sours, the sugar contained in the milk is converted 
by means of bacterial organisms into lactic acid or, as it is further 
distinguished, lactic acid 0} fermentation or sour milk lactic acid. 
This acid is inactive toward polarized light. In the flesh of 
animals another lactic acid has been found which, as just stated, 
is also a-hydroxy-propionic acid or a true lactic acid. This 
acid, however, possesses the characteristic property of activity 
toward polarized light and turns the plane of polarization to 
the right, or as it is termed, it is dextro-rotatory. Also when the 
lactic acid of sour milk which is inactive toward polarized light 
is treated in a definite way (conversion of it into its strychnine 
salt) it has been split into two different lactic acids, one of which 
is active and dextro-rotatory identical with lactic acid from flesh, 
and the other is oppositely active, i.e. is left-handed or levo- 
rotatory. This levo-rotatory lactic acid is also produced 
directly when cane sugar is acted upon by a particular form of 
bacterium. We thus have three isomeric lactic acids all of 
which are the same structurally, i.e. are a-hydroxy-propionic 
acids, viz. inactive lactic acid found in sour milk, dextro lactic 
acid found in animal muscle, levo lactic acid produced by bac- 
terial fermentation of cane sugar. 

How now can we harmonize the existence of three lactic 
acids of identical structure, viz. a-hydroxy-propionic acids, 
CH 3 — CH(OH)— COOH, with our previous statements in re- 
gard to the structure of carbon compounds and with these 
definite properties in connection with polarized light? 

Optical Activity. — Without explaining the physical action 



70 ORGANIC AGRICULTURAL CHEMISTRY 

let it suffice to state that when ordinary white light is passed 
through certain crystalline substances, e.g. quartz and Ice- 
land spar (crystallized calcium carbonate) the rays of light are 
broken into two sets of rays, one called the ordinary ray, the 
other the extraordinary ray. When another crystal or, in 
practice, another half of a crystal reversed, is next interposed, 
the extraordinary ray only passes through the second half of the 
double crystal. In emerging from this double crystal the 
light is found to consist of vibrations all in one plane and is 
said to be polarized. Polarized light then is light which has 
passed through a double crystal of quartz and has been changed 
as described. When such a double crystal has been mounted 
in a particular form of optical apparatus containing a second 
double crystal like the first, it is possible to observe this polar- 
ized light and note how it is affected by different substances. 
Such an instrument is known as a polariscope. 

Now when certain substances, some in crystalline form and 
others in solution, are examined in this instrument, they exhibit 
certain definite characteristic effects upon the polarized light. 
When a solution of ordinary sour milk lactic acid is so examined, 
it is found to have no effect upon the polarized light, i.e. it 
is, as we say, inactive toward polarized light. When, however, 
the structurally identical substance obtained from flesh is simi- 
larly examined, it is found that it turns the plane of the polarized 
light to the right. It is termed, therefore, dextro (right) rotatory. 
In the same way when the third structurally identical lactic 
acid, obtained from cane sugar by the special form of bacterium, 
is examined, it is found to turn the plane of the polarized light to 
the left, and is termed lew (left) rotatory. And when sour milk 
lactic acid, the inactive form, is split by means of its strychnine 
salt, there are obtained both the dextro-rotatory and the levo- 
rotatory compounds. We shall find that other compounds, 
especially tartaric acid and the sugars, possess these same prop- 
erties. It should be emphasized that these differences in physi- 
cal properties as exhibited toward polarized light indicate no 
difference whatever in the chemical structure of the compounds, 



MIXED COMPOUNDS 7 1 

as represented by the groups present or the order of their ar- 
rangement. 

Asymmetric Carbon. — On examining the structural formula 
for the lactic acids, viz. a-hydroxy-propionic acid, we find a 
distinctive fact. 

H 

I 
CH3 - C - COOH Lactic acid 

I 

OH 

We see that the second carbon atom differs from the other two 
in this, that it has united to it four different elements or groups, 
viz., CH 3 , H, OH and COOH. Now it has been found that all 
compounds, which when in solution exhibit optical activity 
toward polarized light, contain at least one carbon atom which 
is thus united to four different elements or groups. The union 
of four different groups to one carbon would give to that car- 
bon in its space relations an unsymmetrical arrangement. Such 
arrangement would make possible an unsymmetrical action 
such as exhibited toward polarized light in that one form is 
right-handed or dextro-rotatory and the other form left-handed 
or levo-rotatory. Such an unsymmetrical arrangement also 
would be like the unsymmetrical nature of the right and left 
hand. This complete unsymmetrical nature would be lost 
whenever any two, or all four, groups united to a carbon atom 
were the same. Furthermore it was found by Pasteur that 
certain compounds, e.g. the salts of tartaric acid, crystallized 
in unsymmetrical or right-and left-handed forms and that these 
right- and left-handed crystal forms when put into solution 
exhibit right- and left-handed action toward polarized light. 

van't Hoff - Le Bel. — This theory as we have outlined it, 
which connects optical activity and the existence of structurally 
identical isomers with the presence in such compounds of an 
unsymmetrical carbon atom, was advanced simultaneously 
by two chemists, van't Hoff, a Dutchman, and Le Bel, a French- 
man. It is known as the theory of the asymmetric (unsymmetrical) 



7 2 



ORGANIC AGRICULTURAL CHEMISTRY 



carbon atom. Le Bel went no further than we have stated above, 
van't HofI, however, not only assumed this asymmetry of the 
carbon atom as the explanation of optical activity and of the 
existence of isomeric structurally identical compounds, but he 
assumed a definite arrangement for such a carbon atom in 
space. 

Tetrahedral Theory. — He assumed that tetravalent carbon 
exists in space situated at the center of a regular tetrahedron 
with the four equal valences directed toward the angles of each 
apex as follows : 




Methane 

In methane all four valences are satisfied with hydrogen so 
that the carbon and the whole compound is completely sym- 
metrical. If, however, as in the lactic acids, these four va- 
lences are satisfied by four different groups, then the carbon 
atom would be asymmetric and the compound would possess 
asymmetry possible of exhibiting itself in its action toward 
polarized light. The formula would be : 



off 




COOH 



HOOG 



Lactic acid 




Such an arrangement would make possible a compound A and 
a second compound B which differ in that one is right-handed 



MIXED COMPOUNDS 73 

and the other left-handed. They are related to each other as 
an object and its image, or as the right hand to the left. It 
can be readily seen that one of these compounds might act 
one way toward polarized light and the other would possibly 
act in the reverse way. By one formula, A for example, we 
can represent the lactic acid of flesh, the dextro-rotatory form, 
and by the other the lactic acid obtained by bacterial action 
on cane sugar, the levo-rotatory form. Thus we can explain 
the two active forms. How about the inactive form? The 
fact that sour milk lactic acid can be split into the two active 
forms, and the same is true of inactive tartaric acid and many 
other inactive compounds which contain an asymmetric car- 
bon atom, gives reason for the view that the inactive compound 
is composed of equivalent amounts of the active forms which 
simply neutralize each other as to their effect upon polarized 
light. 

To state it all briefly : van't Hoff and Le Bel's Theory of the 
Asymmetric Carbon Atom, or, as we also call it, the Tetrahedral 
Theory, explains the existence of three lactic acids by assuming 
that one compound, the dextro-rotatory form, has the space 
arrangement of one of the two formulas just given, say A. 
The other active compound, the levo-rotatory form, has the 
arrangement of the formula B. The third lactic acid, the 
inactive sour milk acid, is composed of equivalent amounts of 
the two active forms. 

Inactive Lactic Acid. — As has been stated before, the inac- 
tive form of lactic acid which is in reality a mixture of the 
dextro and levo forms is found in sour milk. It is produced 
in milk by the bacterial fermentation of the milk sugar which is 
present. 

C12H22O11 + H 2 -> 4 C 3 H 6 3 

Milk sugar Lactic acid 

This reaction consists both of a hydrolysis and of a splitting 
of the molecule. It is brought about by a particular group 
of bacteria, viz. lactic acid bacteria. The acid is also found 



74 ORGANIC AGRICULTURAL CHEMISTRY 

in silage, where it is produced by the bacterial fermentation of 
the carbohydrates present in corn, clover, etc. These carbo- 
hydrates are cane sugar and glucose which are present as such 
or have been formed by the hydrolysis of starch. 

The three carbohydrates, cane sugar, milk sugar and glucose, 
all yield lactic acid by bacterial fermentation. The form of 
acid obtained, i.e. inactive, dextro or levo, depends upon 
the particular bacterial organism which produces the fermen- 
tation. It is probably true that lactic acid is an intermediate 
product in the alcoholic fermentation of glucose into alcohol. 
Lactic acid itself undergoes further bacterial fermentation and 
is converted by the butyric acid ferment into butyric acid, 
C 3 H 7 -COOH. 

+ 2 
2 C 3 H 6 3 -> C 3 H 7 -COOH + 2 C0 2 + 2 H 2 

Lactic acid Butyric acid 

When milk sours and lactic acid is formed, it is the lactic 
acid which causes the coagulation of the protein, casein, present 
in colloidal suspension in the milk and which forms the coagu- 
lum or curd from which cheese is made. 

When pure, inactive lactic acid is a colorless, sirupy liquid 
which absorbs water from the air. It decomposes on heating, 
forming an inner ester called a lactide. It is used as a mordant 
in dyeing in the form of the antimony salt. 

Dextro Lactic Acid (Sarco Lactic Acid). — The dextro-ro- 
tatory variety of lactic acid is the form found in the flesh or 
muscular tissue of animals, from which it gets its name Sarco 
lactic acid. It is also found in the blood and urine. It may be 
prepared by the splitting of the inactive form as previously 
described, or by bacterial fermentation of the sugars previously 
mentioned. 

Levo Lactic Acid. — The levo form of lactic acid is ob- 
tained when cane sugar is fermented with certain lactic acid 
bacteria. It may also be obtained by splitting the inactive 
form. 



MIXED COMPOUNDS 75 



Malic Acid (Mono-hydroxy-succinic Acid) 

We shall now consider three acids which are widely distributed 
in nature occurring either free or as salts in many of our common 
fruits. They all belong to this same group of hydroxy-acids 
to which lactic acid belongs. The first two, malic and tartaric, 
are derivates of succinic acid. 

When succinic acid is converted into mono-brom-succinic acid, 
this, by replacing bromine with hydroxyl by means of silver 
hydroxide, Ag(OH), yields malic acid, thus proving it to be 
mono-hydroxy-succinic acid. The reactions are as follows : 

CH 2 -COOH CHBr-COOH CH(OH)-COOH 

I +Br 2 -» HBr+ | +Ag(OH)-» | 

CH 2 -COOH CH 2 -COOH CH 2 -COOH 

Succinic acid Mono-brom- Malic acid 

succinic acid Mono-hydroxy- 

succinic acid 

In nature malic acid is found in many acid fruits such as 
apples, cherries, gooseberries, raspberries, strawberries, currants, 
pineapples and grapes, and in seeds of some other plants, e.g. 
pepper and parsley and in unripe berries of the mountain ash. 
Its name is derived from its being found in apples. It is ob- 
tained commercially from the mountain ash berries. It is a 
solid substance readily soluble in water and melts at ioo° C. 

The malic acid found in nature is lew-rotatory in dilute solu- 
tions. The dextro-rotatory form and also the inactive form are 
both known. The existence of these three stereo- chemical 
isomers is in accord with the theory just discussed in regard 
to the asymmetric carbon atom, one of the carbon atoms in 
malic acid being asymmetric. 

OH 

I 
H-C-COOH 

I 
CH2-COOH 

Malic acid 



76 ORGANIC AGRICULTURAL CHEMISTRY 

Tartaric Acid {Di-hydroxy-succinic acid) 

Just as we make malic acid from succinic acid through the 
mono-brom-succinic acid so by converting succinic acid into 
the symmetrical di-brom-succinic acid we obtain by means of 
silver hydroxide, Ag(OH), tartaric acid which has, therefore 
the constitution of symmetrical di-hydroxy-succinic acid. 

CH2-COOH CHBr-COOH CH(OH)-COOH 

I + 2 Br 2 ->2HBr+ | + 2 Ag(OH)->| 

CH2-COOH CHBr-COOH CH(OH)-COOH 

Succinic acid Sym. di-brom- Tartaric acid 

succinic acid Sym. di-hydroxy- 

succinic acid 

Tartaric acid is found naturally in the free condition and as 
salts in certain fruits, especially in grapes. Being a dibasic 
acid containing two carboxyl groups or two acid hydrogens, it 
forms salts with either one or both of these hydrogens replaced 
by metals. 
CH(OH) - COOH CH(OH) - COOK CH(OH) - COOK 

I I I 

CH(OH) - COOH CH(OH) - COOH CH(OH) - COOK 

Tartaric acid Mono-potassium tartrate Di-potassium tartrate 

(Acid potassium tartrate) (Neutral potassium tartrate) 

The mono-potassium tartrate or (acid potassium tartrate) 
is the form in which it occurs in grapes and from which source 
it is commercially obtained. When grape juice is fermented 
in preparing wine, there settles out an insoluble material con- 
sisting largely of impure acid potassium tartrate and known as 
argol or crude tartar, the purified acid potassium tartrate being 
known as cream of tartar. The crude tartar is separated, re- 
• crystallized from hot water, converted into the wholly insoluble 
calcium salt and then back into the free tartaric acid which is 
then pure. Tartaric acid as thus obtained forms large trans- 
parent crystals readily soluble in water or alcohol. Several 
of the salts of tartaric acid are commonly in use either in cook- 
ing or in medicine. They are as follows : 

Cream of Tartar, Acid Potassium Tartrate. — This salt of tar- 
taric acid, the formula of which has just been given, is the form 



MIXED COMPOUNDS 77 

in which the acid is found in grapes and is the common domestic 
household article cream of tartar. It is a constituent of most 
baking powders. Its use in cooking is due to its acid character, 
one of the acid hydrogens in tartaric acid still remaining. As 
an acid it reacts in solution with carbonates, such as sodium 
bicarbonate or baking soda, liberating carbon dioxide ; and this 
evolution of carbon dioxide gas expands or raises the dough of 
bread or cake and makes a light porous product. 

Rochelle Salt. — This compound is the mixed potassium 
and sodium salt of tartaric acid, i.e. being dibasic the acid 
has one acid hydrogen replaced by potassium and the other by 
sodium. 

CH(OH) - COOK 

CH(OH) - COONa 

Potassium-sodium tartrate (Rochelle salt) 

The salt forms large crystals containing four molecules of 
water of crystallization. It is a very important reagent as 
a constituent of Fehling's Solution. This will be described 
later in discussing methods of analyzing sugars. It is also 
used in medicine as a constituent of Seidlitz powders, free tar- 
taric acid and sodium bicarbonate being the other constituents. 

Tartar Emetic. — This is a compound of tartaric acid used 
in medicine as an emetic. It is a mixed potassium and anti- 
monyl salt of tartaric acid, one acid hydrogen being replaced 
by potassium and the other by the antimonyl group (SbO). 

CH(OH)-COOK 

I 
CH(OH)-COO(SbO) 

Potassium-antimonyl tartrate (Tartar emetic) 

Free tartaric acid, or its salts, have several properties which 
enable them to be easily detected. When the acid, or a salt 
plus H2SO4, is heated it decomposes, chars, and gives forth 
an odor resembling burnt sugar. When a neutral solution of 
a tartrate is added to an ammoniacal solution of silver nitrate, 



78 ORGANIC AGRICULTURAL CHEMISTRY 

the silver salt is reduced to metallic silver and a silver mirror 
is formed. This reaction is similar to that of aldehyde upon 
silver nitrate. 

Stereoisomerism of Tartaric Acid. — The tartaric acid 
obtained from grapes, as above described, is optically active, 
dextro-rotatory. There is also present with it in grapes the 
inactive form, known as racemic acid, which is also produced 
when tartaric acid is prepared synthetically from succinic acid. 
Racemic acid, like the inactive lactic acid, can be split into its 
two optical components whereby both dextro tartaric acid and 
lew tartaric acid are obtained. This, however, is not all, 
for when tartaric acid is prepared synthetically, or when it is 
heated with water to 165 , a fourth tartaric acid is obtained. 
This tartaric acid is also inactive, but differs from the racemic 
acid in that it cannot be split into its two opposite optical com- 
ponents. It is known as meso-tartaric acid. 

We have then four stereo-isomeric tartaric acids, as follows : 

(1) Dextro tartaric acid in grapes, 

(2) Levo tartaric acid, 

(3) Racemic acid (inactive tartaric acid) found also in grapes, 
can be split into dextro and levo acids, 

(4) Meso-tartaric acid (inactive), cannot be split into two 
components. 

The explanation of these four forms of tartaric acid is analo- 
gous to that of the three lactic acids. The difference between 
tartaric acid and lactic or malic acids, or any other optically 
active substance which we have considered thus far, is that 
while lactic acid has one asymmetric carbon atom, tartaric 
acid has two and these two are directly joined to each other. 

OH 

I 
H-C-COOH 

I 
HO-C-COOH 

I 
H 

Tartaric acid 



MIXED COMPOUNDS 



79 



It is considered possible then that the two halves of the 
compound may be alike in asymmetry and optical power or 
may be opposite. If the two halves of the compound are alike 
they may both be dextro, giving dextro tartaric acid, or they may 
both be levo, making levo tartaric acid. These two in equiva- 
lent amounts would make inactive tartaric acid, which could 
be split into its two components again; that is, racemic acid. 
If, however, the two halves are different, one dextro and the 
other levo, an inactive compound would be formed which 
cannot be split into a dextro and a levo form. This would be 
meso-tartaric acid. 

Thus the existence of four stereo-isomeric tartaric acids is 
possible in accordance with the van't Hoff - Le Bel theory. 
These will be more readily comprehended if we examine the 
four formulas as drawn on a plane surface, or better by an exam- 
ination of models. 



OH 


H 


OH 


H-C-COOH 

| 


HO-C-COOH 


H-C-COOH 

1 


HO-C-COOH 

1 


H-C-COOH 

1 


H-C-COOH 


1 
H 


OH 


OH 


Dextro- 


Levo- 


Meso- 



Racemic 



The stereo-isomerism of these acids is especially interesting 
historically because it was with racemic acid salts that Pasteur 
made the first separation of an optically inactive compound 
into its two opposite optical components and also isolated the 
two enantiomorphic (object and image) forms of crystals, thus 
demonstrating the nature of inactive compounds of this type. 
Such inactive compounds which can be split into optical isomers 
are known now by the general name of racemic compounds. 



80 ORGANIC AGRICULTURAL CHEMISTRY 

Citric Acid 

This is the third hydroxy acid which is found in nature in 
acid fruits. It is especially abundant in fruits of the citrous 
family, lemons, oranges, limes, etc., and is present in as much as 
6 per cent of the juice. It is also produced by a fermentation 
of glucose. It is a solid crystalline compound easily soluble in 
water. The constitution of citric acid is as follows : 

CH 2 -COOH 

I 
C(OH)COOH 

I 
CH 2 -COOH 

Citric acid 

It is thus a mono-hydroxy-tri-carboxy acid, and is tribasic. 

Some of the salts of citric acid have important uses. Agri- 
culturally one salt is of importance in a scientific way. A 
neutral solution of ammonium citrate of approximately 20 
per cent strength is used in fertilizer and soil analysis as a sol- 
vent for the dicalcium or reverted calcium phosphate, the 
phosphoric acid salt which is insoluble in water and yet 
seems to be available to plants. Magnesium citrate is used in 
medicine, and ferric-ammonium citrate is used in making blue 
print photographic paper. 

EXPERIMENT STUDY XVII 

Lactic, Malic, Tartaric, Citric Acids 

(1) (a) Examine samples of lactic, malic, tartaric and citric acids. 
(b) Test acidity toward phenolphthalein indicator, (c) Heat a few 
grams of tartaric acid or a salt of tartaric acid with sulphuric acid in 
a test tube. Note the odor of burnt sugar, (d) Prepare a little 
ammoniacal silver nitrate (silver nitrate and just enough NH 4 OH to 
dissolve the precipitate first formed). To this add a few drops of 
tartaric acid or a tartrate and warm. Note reduction of silver nitrate 
to metallic silver. 



MIXED COMPOUNDS 8 1 

(2) (a) Examine samples of 

Potassium acid tartrate (Cream of tartar), 
Potassium sodium tartrate (Rochelle salt), 
Potassium antimonyl tartrate (Tartar emetic). 

(b) Mix about 5 g. each of potassium acid tartrate and sodium acid 
carbonate, NaHC0 3 . Add 10 c.c. water and warm slightly. What 
gas is given off ? This mixture is the basis of most baking powders. 



CHAPTER VI 

AMINO-ACIDS, PROTEINS, UREA AND 
URIC ACID 

AMINO-ACIDS 

The amino compounds and derivatives which we have thus 
far considered have been first the alkyl-amines in which an 
alkyl group {e.g.) methyl, ethyl, propyl, etc., has been substi- 
tuted in ammonia for one hydrogen yielding a substituted 
ammonia compound. These show a close relationship to 
ammonia in many of their reactions, especially the formation 
of ammonium-like salts. The compounds are also to be con- 
sidered as amino substitution products of the hydrocarbons in 
which the amino radical NH 2 is substituted for one hydrogen in 
a hydrocarbon. Methyl amine is also, therefore, ammo-methane. 

H 
N^-H or H-C-NH 2 

\h I 

H 

Methyl amine Amino-methane 

As amino substituted hydrocarbons, the amines are thus exactly 
analogous to the halogen and hydroxy substitution products. 

CH 3 - CI CH 3 - OH CH 3 - NH 2 

Mono-chlor-methane Hydroxy-methane Amino-methane 

In connection with the derivatives of acids we considered 
also the acid amides in which the hydroxyl portion of the car- 
boxyl group was replaced by the amino group. 

CH 3 - COOH -> CH 3 - CONH 2 

Acetic acid Acet-amide 

Now just as we have mixed compounds which contain both 
halogen and carboxyl or both hydroxyl and carboxyl groups, 

82 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 83 

the latter of which we have just been considering and which 
we have termed the hydroxy-acids, so also we have mixed com- 
pounds containing amino and carboxyl groups which, similarly, 
we know as amino-acids. 

CH 3 - COOH, CH 2 C1- COOH, CH 2 (OH) - COOH, CH 2 (NH 2 ) - COOH 

Acetic acid Chlor-acetic acid Hydroxy-acetic acid Amino-acetic acid 

These amino-acids are acids in which a hydrogen of the radi- 
cal is replaced by the amino group. This substitution may 
take place in any one of the carbon groups composing the 
hydrocarbon radical of the acid. The hydroxy-acids are both 
alcohol and acid compounds and the amino-acids similarly 
possess the properties of both acids and amines. As acids they 
form salts, both metallic salts and esters, also acid chlorides 
and acid amides. As amines they form amine or ammonium 
salts with acids. They also react like ammonia with acid 
chlorides, yielding acid amides in which the amino-acid less one 
of the amine hydrogens replaces the hydroxyl group of another 
acid. They may be prepared directly from the halogen acids 
by the action of ammonia. 

Taking one of the simpler compounds, e.g. amino-acetic 
acid, as an illustration, these relations may be clearly shown. 

CH3-COOH -> CH 2 Cl-COOH+NH 3 -> CH 2 (NH) 2 -COOH+HCl 
Acetic acid Chlor-acetic acid Amino-acetic acid 

CH 2 (NH 2 ) - COOR 

Ester 

CH 2 (NH 2 ) - COONH4 

Ammonium salt (metal salt like 
ammonium acetate) 

CH 2 (NH 2 ) - COOH^ -CH 2 (NH 2 ) - CONH 2 

Amino-acetic acid \^\ Acid amide 

CH 2 NH 2 .HCl-COOH 

Hydrochloride (Amine salt like 
methyl amine hydrochloride) 

CH 2 -COOH 

I 
NH-OC-R 

Acyl-amino-acid 





84 ORGANIC AGRICULTURAL CHEMISTRY 

Glycine. Amino-acetic Acid. CH 2 (NH 2 ) — COOH 

When this compound is prepared from chlor-acetic acid by 
the action of ammonia, the ammonium salt of the amino-acid 
is formed. 

CH 2 C1 - COOH + 2 NH 3 CH 2 (NH 2 ) - COONH 4 + HC1 

Chlor-acetic acid Ammonium salt of amino-acetic acid 

This salt, when boiled with hydrochloric acid, decomposes and 
forms the amine hydrochloride of the acid. 

CH 2 (NH 2 )-COONH4+2HCl -» CH 2 (NH 2 HC1)-C00H+NH4C1 

Ammonium salt of amino-acetic acid Hydrochloride of amino-acetic acid 

Amino-acetic acid is a solid crystalline compound melting 
at 23 5 C. It is readily soluble in water. The hydrochloride 
salt is also a crystalline solid soluble in water. An important 
derivative of amino-acetic acid should be mentioned. As 
previously stated the amino group in the compound acts as 
ammonia and forms compounds in which the amino residue 
becomes the amide part of an acid amide. With acetic acid 
or, better, with the acid chloride of acetic acid, ammonia and 
amino-acetic acid yield the following : 

CH3 - COC1 + NHg ->■ CH 3 - CONH 2 + HC1 

Acetyl chloride Ammonia Acet-amide 

CH3-COCl+(NH 2 )-CH 2 -COOH -> CH 3 -CO-NHCH 2 -COOH+HCl 
Amino-acetic acid Acetyl-amino-acetic acid 

Benzoic acid is a mono-carboxy acid derived from the hydro- 
carbon benzene, C 6 H 6 . It is CeH 5 — COOH. This forms a 
'benzoyl (C 6 H 5 CO) derivative of amino-acetic acid. 

C 6 H 5 - COOH C 6 H 5 CO - (NH) CH 2 - COOH 

Benzoic acid Benzoyl-amino-acetic acid (Hippuric acid) 

This compound, benzoyl-amino-acetic acid, is the substance known 
as hippuric acid. It is a constituent of the urine of man but 
is more abundant in that of horses and cows and of other herbiv- 
orous animals. When hippuric acid is boiled with hydrochloric 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 85 

acid it hydrolyzes, forming benzoic acid and amino-acetic acid. 
The free amino-acetic acid then with the HC1 yields the hydro- 
chloric acid salt. 



CeHs-CO 

+ 
HO 



NH-CH2-COOH 

-> C 6 H 5 -COOH+(NH 2 )CH 2 -COOH 

Benzoic acid Amino-acetic acid 



Hippuric acid+ILO 

Hippuric acid is important as a product of animal metabolism 
and will be considered again under that subject. Amino- 
acetic acid commonly goes by another name, especially in con- 
nection with its physiological relationships. It is known as 
glycine; the prefix, glyc, of this name indicates its sweet taste, 
and the termination, ine, its amine nature. 
Alanine, a-amino-propionic acid : CH 3 — CH(NH 2 ) - COOH 

This compound, the next higher homologous amino-acid, is 
the amino analogue of lactic acid. 

Lactic acid, a-hydroxy-propionic acid: CH3— CH(OH) — COOH 
Alanine, a-amino-propionic acid : CH3 — CH(NH 2 ) — COOH 

Like lactic acid, it contains an asymmetric carbon atom (under- 
lined) and possesses optical activity, being known in its dextro, 
levo and inactive forms. The compound is similar to glycine 
in its properties, being a solid crystalline compound forming 
salts with both bases and acids, and also derivatives of the acid 
amide type as discussed under glycine. 

Higher Amino-acids 

A few other amino-acids will be mentioned, simply giving 
their constitutional formulas, in order that they may be referred 
to later. 

Valine, a-amino-/3-methyl-butyric acid : 

CH3 - CH - CH(NH 2 ) - COOH 

I 
CH 3 



86 ORGANIC AGRICULTURAL CHEMISTRY 

Leucine, a-amino-y-methyl-valeric acid (a-aminoiso-caproic 
acid) : 

CHsv 

>CH - CH 2 - CH(NH 2 ) - COOH 
CH 3 X 

Iso-leucine, a-amino-/3-methyl- valeric acid : 

CH 3 - CH 2 - CH- CH(NH 2 ) - COOH 

I 
CH 3 

Serine, a-amino-/3-hydroxy-propionic acid : 

CH 2 (OH) - CH(NH 2 ) - COOH 
Lysine, a-e-di-amino-caproic acid : 

CH 2 (NH 2 ) - CH 2 - CH 2 - CH 2 - CH(NH 2 ) - COOH 
Aspartic acid, amino-succinic acid : 

CH(NH 2 ) - COOH 

CH 2 -COOH 

Asparagine, mono-amide of amino-succinic acid: 

CH(NH 2 ) - COOH 

I 
CH 2 -CONH 2 

This compound is both an amino-acid and an acid amide. 
Glutamic acid, a-amino-glutaric acid : 

CH(NH 2 ) - COOH 

CH 2 

I 
CH 2 -COOH 

Phenyl-alanine, a-amino-/3-phenyl-propionic acid : 

CH 2 -CH(NH 2 )-COOH 

I 
CeH 5 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 87 

Tyrosine, a-amino-/3-hydroxy-phenyl-propionic acid : 
CH 2 -CH(NH 2 )-COOH 

C 6 H 4 (OH) 
Tryptophane, a-amino-/3-indol-propionic acid: 

CH 2 -CH(NH 2 )-COOH 

I 

(C 8 H 6 N) (Indol group) 

Arginine, a-amino-5-guanidine-valeric acid: 

CH 2 - CH 2 - CH 2 - CH(NH 2 ) - COOH 



HNC 



NsTI 



L2 

(Guanidine residue) 



PROTEINS 

The three essential organic or carbon-containing constituents 
of animal foods sue fats, e.g. lard, tallow, olive oil; proteins, e.g. 
egg albumin, cheese casein and wheat gluten ; and carbohydrates, 
e.g. sugar, starch and cellulose. Fats we have already dis- 
cussed in a preceding chapter. The consideration of proteins 
should come in connection with the amino-acids which we have 
just studied. The carbohydrates will be taken up a little later. 

The three food constituents above mentioned are alike in 
that they all contain the three elements, carbon, hydrogen and 
oxygen. When we come to study the manner in which these 
foods are used in the animal body, we shall find that this use 
rests fundamentally upon the property of these compounds to 
be oxidized, and by means of this oxidation to furnish the energy 
of the animal body. The oxidation of these substances depends 
upon the carbon and hydrogen contained in them. As these 
food constituents are practically the only compounds which 
the animal body thus uses as a source of energy, they are of the 
utmost importance, and their presence determines the value 



88 ORGANIC AGRICULTURAL CHEMISTRY 

and use of any foodstuff. All this will be considered again at 
greater length in the later part of our study. 

Now, while proteins are like fats and carbohydrates in con- 
taining carbon, hydrogen and oxygen, they differ from them 
in containing also the element nitrogen. Protein, as the name 
signifies, is the primary or fundamental substance of living 
matter. It is one of the chemical constituents of the biological 
substance protoplasm, which is the essential of all living cells. 
As we shall find later, animals are unable to use the element 
nitrogen for the purpose of forming new protein unless that 
nitrogen is in the form of protein itself or of compounds very 
closely related to protein. That is, to form animal protein, 
food protein is essential. We thus see how important a place 
the substances we call proteins occupy in connection with plant 
and animal life. What then are these proteins in their chemi- 
cal nature? 

While in most cases proteins contain only the four elements 
carbon, hydrogen, oxygen and nitrogen, they are among the 
most complex compounds in organic chemistry. In addition 
to being very complex, their physical and chemical properties 
are such that they are among the most difficult of all compounds 
to study. From the examples of proteins previously given, 
viz. egg albumin or white of an egg, cheese curd or casein and 
wheat gluten, the tough elastic constituent of wheat left when 
the starch is washed away, we see that these substances are 
of a somewhat different nature from that of ordinary chemical 
compounds. In fact, we have hardly any evidence that any 
one of the substances we know as a protein is a single individual 
compound. Some proteins are definitely known to be complex 
mixtures of several individuals, and probably no one of them 
can be definitely considered as an individual. 

Physical Properties of Proteins 

The physical properties of proteins are in general those of 
non-crystallizable (though some have been crystallized) colloidal 
compounds. They do not have definite melting points or boil- 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 89 

ing points, and their chief differences from each other lie in 
their slightly different solubility. The classification of proteins 
has thus been based largely upon these slight differences in 
solubility and upon certain general properties. The differences 
in solubility are also not sharp, as in the case of many crystal- 
line, gaseous and liquid compounds, so that their sharp separa- 
tion is an impossibility. Differences in solubility such as have 
been used to distinguish proteins from each other have given 
us certain groups such as the following : 

Albumins, soluble in water, 
Globulins, soluble in dilute salt solutions, 
Prolamines, soluble in dilute alcohol, 
Albuminoids, insoluble in all neutral solvents, 
etc. 
The solubility in water may be easily tested with such pro- 
teins as egg albumin, wheat gluten and milk casein, as in Experi- 
ment Study XVIII, 1. This is also shown in Experiment Study 
XXIX, by the separation of the proteins in milk where we ob- 
tain milk albumin which is soluble in water, and milk casein, 
a phospho-protein which is insoluble in water. 

A few proteins are more complex than the ones given above, 
classified by differences of solubility, and these are known as 
double or conjugated proteins. They contain two distinct 
parts and are distinguished by the parts shown to be present 
as follows : 

Gly co-proteins, protein and a carbohydrate (mucin in saliva), 
Nucleo-proteins, protein and nucleic acid, 
Phospho-proteins, protein and a phosphorus compound 

(casein), 
Haemoglobins, protein and an iron-containing compound 

(blood haemoglobin). 

We thus see how difficult a matter it is to arrive at any con- 
clusion as to the true chemical nature of proteins from a study 
of their physical properties because they each lack the sharply 
distinctive properties of ordinary chemical compounds. 



QO ORGANIC AGRICULTURAL CHEMISTRY 

Chemical Properties of Proteins 

Composition. — When we turn to the chemical properties 
of proteins we find that here too we have much less to work with 
than in most cases. Chemically proteins are characterized by 
their inactivity and by the difficulty with which they are con- 
verted into other compounds. In their ultimate composition 
also there is little to aid in their study. The analysis of many 
proteins has given results as follows : 

Carbon 5i~55 per cent 

Hydrogen 6-7 per cent 

Nitrogen 1 5-1 7.6 per cent 

Oxygen 20-25 per cent 

Sulphur 0.3-2.5 per cent 

Analysis. — Nitrogen, the characteristic element in proteins 
which distinguishes them from carbohydrates and fats, may be 
easily detected by test as in the experiment study following. 
A positive test for nitrogen does not prove an organic substance 
to be protein, but it does distinguish proteins from the other 
two organic food constituents. The quantitative determination 
of nitrogen in materials which contain protein, such as most plant 
or animal substances, is the only analytical method known for 
determining the protein itself. The method universally used 
is known as the Kjeldahl method for nitrogen as described in 
the experiment study below. 

Qualitative tests are also made for proteins by means of 
reagents which give color reactions or precipitations. In gen- 
eral all proteins respond to these tests, while in some cases cer- 
tain non-protein compounds also respond. While some of the 
color reactions have been shown to be due to certain organic 
groups it is, nevertheless, impossible to differentiate proteins by 
these reactions. 

Molecular Weight. — When an effort has been made, based 
upon the percentage composition of the proteins, to arrive at 
some idea as to the size of the molecule of the compounds, 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 91 

some very striking and interesting results have been obtained, 
but which really give us very little information of value. Molec- 
ular weights have been assigned as follows : 

Edistin, based on the per cent of sulphur present . . 14,530 

Egg albumin, based on the per cent of sulphur present 15,703 
Blood serum albumin (horse) based on the per cent of 

sulphur present 14,989 

Blood oxy-haemoglobin (horse) based on the per cent 

of sulphur present 1 6,655 

Blood oxy-haemoglobin, based upon iron content . . 15,000 

This discussion so far, though it gives us no clear idea as to 
the real chemical nature of the proteins, at least shows us very 
clearly how complex the compounds are and how difficult the 
study of them is. 

Hydrolytic Decomposition. — Only one line of investigation 
has resulted in throwing any light on the subject. When pro- 
teins are boiled with acids or alkalies, hydrolysis takes place by 
addition of water and the splitting of the complex compounds 
into simpler compounds. These simpler compounds are the 
amino-acids which we have just considered. This explains 
why the study of the proteins is taken up at this point, imme- 
diately following that of the amino-acids. We have given the 
formulas for thirteen amino-acids. In addition to these thir- 
teen, five others are known, making a total of eighteen, all of 
which have been isolated as products formed by the hydrolytic 
cleavage of proteins. These different amino-acids are obtained 
in varying proportions by the hydrolysis of different proteins. 
This gives a better basis for separating or distinguishing different 
proteins than can be obtained from a study of physical prop- 
erties. 

It seems, therefore, that as all proteins yield these amino- 
acids as cleavage products, some proteins yielding nearly the 
entire eighteen, the proteins themselves are probably com- 
posed of these compounds as constituent parts. 



92 ORGANIC AGRICULTURAL CHEMISTRY 

Poly-peptides 

The question then arises, how may these amino-acids be 
joined together to form the proteins? In our discussion of 
amino-acids it was emphasized that the peculiar characteristic 
of them is that they are both acid and basic compounds in the 
same molecule. The amino group, acting as ammonia, forms 
amide compounds with organic acids. This is illustrated by 
the formation of the benzoyl derivative of amino-acetic acid in 
which the radical of benzoic acid replaces one of the hydrogens 
of the amino group. The product, benzoyl-amino-acetic acid, or 
benzoyl-glycine, is hippuric acid. 

CH 3 - CHNH(H) - COOH CH3 - CH(NH) - COOH 

Amino-acetic acid (glycine) 

+ -> I 

C 6 H 6 -CO(OH) - H 2 C6H5 -CO 

Benzoic acid Benzoyl-glycine (hippuric acid) 

Now it has been found that by certain reactions two molecules 
of amino-acetic acid react with each other, the amino group in 
one reacting with the carboxyl group of the other just as above, 
and a compound is obtained as follows : 

CH 3 -CH -NH(H) -COOH CH 3 -CH(NH) -COOH 

+ -> I 

CH 3 -CH(NH 2 ) -CO(OH) CH, -CH(NH 2 ) -CO 

Glycyl-glycine 

The compound formed is known as glycyl-glycine, exactly analo- 
gous to benzoyl-glycine, and is it called a di-peptide. 

In a similar way some 30 compounds have been prepared by 
joining together certain amino-acids. Not only, however, may 
two amino-acids be thus united (the amino-acids being the same 
or different), but 3, 4, 5, 6, 8, 10, 14 and finally 18. These are 
known as tri-peptides, tetra-peptides, deca-peptides , octa-deca- 
peptides, etc., depending upon the number of amino-acids united. 
As a class they are known as poly-peptides. 

Now the important fact is that these poly-peptides exhibit 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 93 

characters very similar to those of proteins. By hydrolysis 
they yield the amino-acids from which they have been prepared. 
They give color reactions and precipitation tests similar to 
those given by proteins. Finally they have been obtained as 
intermediate cleavage products between the proteins themselves 
and the amino-acids. Absolute identity of a poly-peptide made 
synthetically and one obtained as a cleavage product of a 
protein has not yet been established, but the evidence points 
strongly to the conclusion that proteins are poly-peptides of the 
various amino-acids obtained as cleavage products. 



EXPERIMENT STUDY XVIII 

Proteins 

(1) Solubility. Test solubility of egg albumin, wheat gluten and 
milk casein in water. Compare also Experiment Study XXIX on 
the separation and isolation of milk proteins. 

(2) Proof of Nitrogen in Proteins, (a) Place about a gram or two 
of protein (egg albumin) in a dry test tube. Add about an equal 
volume of fine soda lime. Heat. Hold a piece of red litmus paper at 
mouth of tube. Also notice odor. Ammonia is liberated, proving 
nitrogen in the original protein. 

(b) Place a small amount of protein (egg albumin) in a small piece 
of glass tubing closed at one end. Add a piece of metallic sodium. 
Heat red hot for some time. Place end of hot tube in a little water 
to crack it and let fused mass into the water. Boil. Add a drop of 
HC1 and 5 c.c. of FeCl3. Now add a little FeS0 4 . A blue precipitate 
proves presence of CN group as Na 3 Fe(CN) 6 . The N came from the 
protein. 

(3) Quantitative Determination of Protein, (a) Place 0.5 g. of 
pure protein, e.g. egg albumin, casein or wheat gluten, or 1.0-5.0 g. 
of a protein-containing plant or animal substance, e.g. wheat, cotton- 
seed meal, meat, or milk, in a long-necked, round-bottom flask 
(Kjeldahl flask). Now add 25-30 c.c. concentrated pure sulphuric 
acid and 10 g. crystallized potassium sulphate. Heat gradually in a 
hood until the acid boils, being careful to avoid frothing. Continue 
heating until the organic substance is all oxidized and a light straw- 



94 ORGANIC AGRICULTURAL CHEMISTRY 

colored or colorless liquid remains (usually 2-5 hours' heating is re- 
quired). Cool the contents of the flask. Add quickly about 200 
c.c. water and then about 50 c.c. concentrated (50 per cent) sodium 
hydroxide solution and connect the flask at once with a condenser. 
The receiver end of the condenser should dip below the surface of the 
liquid in the receiving flask. This liquid is water plus a known 
amount of standard (iV/10 usually) hydrochloric acid sufficient to 
more than neutralize all ammonia distilled over. Distill the con- 
tents of the digestion flask long enough to drive over all ammonia 
(usually I to 1 hour). Titrate back excess of acid and calculate 
the amount of ammonia, or of nitrogen, obtained from the original 
protein substance used. 

(b) Reactions of Kjeldahl Determination of Nitrogen in Protein. 
The Kjeldahl method for determining nitrogen is applicable to all 
protein substances and has been modified in various ways to adapt 
it to various nitrogen compounds such as nitrates, etc. It is the 
universal method for determining nitrogen in practically all agricul- 
tural analysis of such materials as plant and animal substances, fer- 
tilizers, soils, etc. The details in regard to the method and its 
modifications will be found in any book on analytical chemistry or 
agricultural analysis. 

The modification given in this study is known as the Gunning 
modification. The principle of the method is in general as follows : 
When an organic nitrogen-containing compound, such as a protein, is 
heated to the boiling point with concentrated sulphuric acid, the pro- 
tein is completely decomposed and all carbon and hydrogen are oxidized. 
All of the nitrogen is converted into ammonia, which in the presence 
of the sulphuric acid forms ammonium sulphate, which is non-volatile 
and is thus not lost in the digestion. The potassium sulphate added 
to the sulphuric acid in the Gunning modification is for the purpose 
of raising the boiling point of the acid, thus increasing the oxidation 
power or its rapidity. When the digestion begins much carbon is 
set free which gradually disappears as oxidation proceeds. When 
the digested material is colorless or straw color, the carbon is all 
oxidized and usually all nitrogen compounds have by this time been 
converted into ammonia and the digestion is complete. At the com- 
pletion of digestion, therefore, all of the protein nitrogen is in the 
digestion liquid in the form of ammonium sulphate. After cooling 
and dilution, strong sodium hydroxide is added sufficient to more 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 95 

than neutralize the excess of the sulphuric acid. The sodium hydrox- 
ide reacts with the ammonium sulphate, setting free the ammonia. 
This ammonia is then distilled into standard acid and the amount 
of standard acid which is thus neutralized by the ammonia is deter- 
mined by titration against a standard alkali. From the amount of 
standard acid neutralized the amount of ammonia is calculated. 
From this amount of ammonia, the amount of nitrogen is calculated, 
and this amount of nitrogen is the whole of the nitrogen contained 
in the original protein. 

On the average, as previously stated, proteins contain 16 per cent 
nitrogen. Therefore, multiplying the amount of nitrogen by the 
factor 6.25 gives us the amount of protein in the original substance. 
This factor, 6.25, is the one commonly used for converting nitrogen 
into protein, and agricultural analyses in general are calculated with 
this factor which may be understood unless otherwise stated. Some 
proteins contain more than 16 per cent nitrogen, e.g. the proteins 
of wheat gluten contain 17.6 per cent nitrogen. The factor for con- 
verting into protein would be, then, 5.68. The following typical 
analysis may be given as an illustration of the calculation. 

(c) Calculation of a Kjeldahl Nitrogen Determination. 

Milk taken = 5.000 g. 

N/10 HC1 in receiver = 25.0 c.c. 

N/10 NaOH used in titration = 6.1 c.c. 
N/10 HC1 neutralized = 18.9 c.c. 

1 c.c. N/10 HC1 contains 

.00364 g. HC1 
.*. 18.9 X .00364 = 0.0688 g. HC1 

HC1 : NH 3 : : .00364 : .0017 
.*. .0688 g. HC1 = 0.0321 g. NH 3 

NH 3 :N : : 17 : 14 

.*. .0321 g. NH 3 EE 0.0265 g- N. 

Protein factor = 6.25 

.'. .0265 X 6.25 EE 0.1656 g. Protein 

.1656 g. Protein 
in 5.0 g. milk = 3.31 per cent = protein in milk 

(4) Color Reactions of Proteins. (See list of proteins at end of 
this experiment.) (a) Millon's Reaction. Millon's Reagent is pre- 
pared as follows: Dissolve one part by weight of mercury in two 



96 ORGANIC AGRICULTURAL CHEMISTRY 

parts by weight of concentrated HN0 3 (sp. gr. 1.42) and then dilute 
with two vol. H 2 0. To a small amount of solid protein in a test 
tube add a few drops of Millon's reagent. Warm. A yellow or 
white color which turns red on heating indicates protein. The test 
works best on solid protein. The test is obtained with any sub- 
stance containing the hydroxy -phenyl group (C 6 H 4 (OH)) so that non- 
proteins like tyrosine, phenol or carbolic acid (CeH 5 OH) and thymol 
give a positive test. 

(b) Xanthoproteic Reaction. To a small amount of protein in a 
test tube add concentrated nitric acid. A white precipitate turning 
yellow indicates protein. Cool and add ammonium hydroxide. The 
color changes to orange. The reaction depends upon the presence of 
the phenyl group (C5H5— ) so that any phenyl-containing compound 
such as tyrosine, phenylalanine and tryptophane, phenol, etc., gives a 
positive test. The yellow color produced when nitric acid stains the 
flesh is due to this reaction. 

(c) Biuret Reaction. To a 5 c.c. solution of protein add an equal 
volume of concentrated KOH or NaOH. Mix thoroughly. Make a 
very dilute solution of copper sulphate by adding a few drops (2 to 5) 
of ordinary 10 per cent solution copper sulphate to a test tube full of 
water. The dilute CUSO4 should be only very faintly blue. Now 
add a few drops of this dilute CUSO4 to the alkaline protein solution 
and warm. A pink-violet color indicates protein. The reaction is 
due to substances containing two amino (NH 2 ) groups. These groups 
may be joined together directly or with an intermediate carbon 
group. Biuret, the substance which gives the name to the reaction, 
is formed from urea by the loss of ammonia (see Experiment XIX). 

Test by the above reagents : 

(a) Egg albumin, fresh, (e) Milk casein or curd, 

(b) Dilute solution of egg albumin, (J) Wheat gluten, 

(c) Egg albumin, dry, (g) Dried blood, 

(d) Egg albumin, coagulated (h) Horn or hair or finger nail. 

(cooked), 

(5) Precipitation Tests, (a) To 5.0 c.c. of dilute mercuric chloride 
(corrosive sublimate) solution, add a little egg albumin solution. 
Note the precipitation of mercury albuminate, (b) Repeat the ex- 
periment, using lead acetate solution instead of mercuric chloride. 
The precipitate here is lead albuminate. These two experiments 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 97 

illustrate the property of proteins to form salts known as albu- 
minates, and on this property is based the use of egg albumin as an 
antidote for poisoning with mercuric chloride or lead salts. 



UREA, URIC ACID AND PURINE BASES 

Urea is one of the end products of the metabolism of protein 
in the animal body. When body protein, having been built 
up from food protein, is burned in the body for the production of 
muscular energy or of body heat, part of the carbon is oxidized 
to carbon dioxide, part of the hydrogen to water, and the rest 
of the carbon, hydrogen and oxygen are eliminated through the 
kidneys in the form of urea, uric acid, creatinine, purine bases 
(xanthine), etc. These compounds in addition to carbon, 
hydrogen and oxygen contain all of the nitrogen of the original 
food or body protein. Their importance in animal physiology 
is, therefore, apparent. 

Urea 

What now is urea? The composition is CH4N2O and it has 
been shown to have the constitution of a di-amide of hypothetical 
carbonic acid. 

/NH 2 /OH 

= C< = C< orH 2 C0 3 

N NH 2 x OH 

Urea Carbonic acid 

The compound may also be denned or considered as amino- 

formamide. 

H-COOH NH 2 -COOH NH 2 -CO-NH 2 

Formic acid Ammo-formic acid Amino-formamide 

This constitution may be proven in several ways. Amino- 
formic acid is the very simplest of the amino-acids. 

H-COOH NH 2 -COOH 

Formic acid Amino-formic acid 



98 ORGANIC AGRICULTURAL CHEMISTRY 

This acid is not known as the free acid, but is known both in 
the form of its ammonium salt and also of its ethyl ester. 

NH 2 -COONH 4 NH2-COOC2H5 

Ammonium amino-formate Ethyl amino-formate 

Now when ammonium amino-formate is heated, water is lost 
and urea results. Also when ethyl amino-formate is treated 
with ammonia, urea is formed and ethyl alcohol is the other 
product. These reactions leave no doubt as to the structure of 
urea and its relation to formic acid. 

NH 2 -CO(0)NH 2 (H 2 ) -> NH 2 -CO -NH 2 + H 2 

Ammonium amino-formate Urea 

NH 2 -CO(OC 2 H 5 +H)NH 2 -> NH 2 -CO -NH 2 + HO -C 2 H 5 

Ethyl amino-formate Urea Alcohol 

The relation of urea to carbonic acid is also shown by this first 
synthesis above, for the ammonium amino-formate is produced 
when carbon dioxide and ammonia are brought together. 

/NH 2 
C0 2 + 2NH 3 ->C = 

\ONH 4 

Ammonium amino-formate 
Ammonium carbamate 

As this compound in its relation to carbonic acid is both an acid 
amide and an ammonium salt, it is known also as ammonium 
carbamate. This with a molecule of water forms ammonium 
carbonate. 

/NH 2 /ONH4 

C = O + H 2 -» C = O or (NH 4 ) 2 C0 3 

\ONH 4 \ONH 4 

Ammonium carbamate Ammonium carbonate 

Carbonic acid though not existing free is known as its di-ethyl 

ester. 

/OC 2 H 5 
OC< 

x OC 2 H 5 

and this compound with ammonia forms urea and alcohol. 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 99 

.(OC2H5 H)NH 2 /NH 2 

OC< + -*OC< +2C2H5OH 

\OC 2 H 5 H)NH 2 X NH 2 

Di-ethyl carbonate Urea 



Also carbonyl chloride (phosgene), COCl 2 , yields urea with 

ammonia. 

H)NH 2 /NH 2 

CO(Cl 2 + ->OC< 

H)NH 2 X NH 2 

Carbonyl chloride Urea 



Thus the relationship of urea to both carbonic acid and formic 
acid is established. 

The most interesting synthesis of urea is one which shows 
little as to its constitution, but which is important because it 
was the first preparation, from purely inorganic substances, of 
a compound found in animals or plants. In 1828 the German 
chemist Wohler obtained urea by simply heating the inorganic 
salt ammonium cyanate. In this conversion no other substance 
was added or produced, there simply being a rearrangement of 
the atoms. 

/NH 2 
NH 4 0-CN->OC< 

X NH 2 

Ammonium cyanate Urea 

Up to the time of this historic synthesis no substance known 
only as a product of living organisms or, as they were termed, 
vital products, had ever been prepared in the laboratory. 
This caused the abandonment of the view that organic sub- 
stances belonged to a different class, and needed the presence 
of a different kind of chemical reaction than inorganic sub- 
stances. The vital force, as it was called, was not essential 
to the formation of organic compounds. This is not saying, 
however, that living matter itself can be produced from non- 
living matter. Wohler's synthesis of urea thus stands as an 
epoch-making discovery, and marks the real beginning of a 
new era in organic chemistry. 



IOO ORGANIC AGRICULTURAL CHEMISTRY 

Urea occurs in considerable amounts in the urine of all ani- 
mals. In man the amount is about 25 grams or one ounce per 
day. It is present in urine in a much larger quantity than any 
of the other nitrogenous constituents, all of which, as previously 
stated, result from the metabolism of body protein or food pro- 
tein, and they contain all of the nitrogen of the protein metabo- 
lized. They are true excretion or waste products. 

Urea is a beautiful crystalline compound forming needle-like 
prisms, melting at 13 2 C. It is readily soluble in water and in 
alcohol. It may easily be isolated from urine, first as the nitric 
acid salt, and this converted into free urea (Exp. XXXI). 
When urea is heated with water to 180 C. or when it is 
boiled with acids, hydrolysis occurs, and ammonium carbonate 
is first formed, which then breaks up into ammonia and 
carbon dioxide. 

y NH 2 /ONH 4 

OC< + 2 H 2 -> OC< -> C0 2 + 2 NH3 +H2O 

X NH 2 X)NH 4 

Urea Ammonium carbonate 

Probably ammonium carbamate (ammonium amino-formate) 
is the intermediate product between urea and ammonium car- 
bonate. This decomposition is the reverse of the reaction of 
synthesis of urea from ammonia and carbon dioxide. The 
importance of this decomposition is that it takes place natu- 
rally due to the action of bacterial organisms., urea bacteria. 
When urine undergoes fermentation, this reaction occurs and 
the nitrogen of the urea, which is the nitrogen of the original 
body or food protein, is thus set free in the form of ammonia. 
This ammonia, which in some cases is useful as a plant food, 
becomes readily converted by bacterial organisms into nitric 
acid and its salts, in which form all plants can utilize it. 
Thus, by these fermentation changes, nitrogen of urine, the 
chief nitrogenous substance in ordinary manure, and which has 
derived its nitrogen from the protein food, becomes converted 
into forms directly available to plants. 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID IOI 

Biuret. — This compound, as the name indicates, is a deriva- 
tive of two molecules of urea from which it is formed by the 
loss of one molecule of ammonia. The reaction is as follows : 



oc/ 



NH 2 

/NH 2 
X NH(H) OC< 



./ 



NH + NH 3 



y (NH 2 ) OC< 
OC< X NH 2 

X NH 2 

2 Urea Biuret 



The substance is colored pink by a very dilute solution of 
copper sulphate, and the biuret test for proteins (Experiment 
Study XVIII, 4, c) derives its name from this compound. 

EXPERIMENT STUDY XIX 

Urea 

(i) Determination of Urea, (a) Make a 2 per cent solution of 

urea, (b) Prepare an alkaline solution of sodium hypobromite as 

follows : 

NaOH, 10 per cent solution, 100 c.c. 

Bromine 2 c.c. 

2 NaOH + Br -> NaOBr + NaBr + H 2 

(c) Fill the ureometer tube with the hypobromite solution and then 
add, by means of a small 1 c.c. bent pipette, 1 c.c. of urea solution 
to the ureometer tube. Allow to stand and measure the gas evolved. 
The gas is nitrogen according to the following reaction : 

y NH 2 
OC< + 3 NaOBr -> N 2 + 2 H 2 + C0 2 + 3 NaBr 

N NH 2 

Urea (mol. wt. 60) Nitrogen (mol. wt. 28) 

The C0 2 evolved is absorbed by the alkali of the solution. This 
reaction is quantitative and the amount of nitrogen gas evolved is 
an exact measure of the urea decomposed as 60 parts by mass of urea 
yield 28 parts by mass of nitrogen. The ureometer used in this test 
is a piece of clinical apparatus so graduated that for 1 c.c. of urine the 
nitrogen evolved is read directly in per cent of urea in the urine. 



102 ORGANIC AGRICULTURAL CHEMISTRY 

(2) Preparation of Biuret. Place a small amount of urea in a dry, 
small test tube. Heat carefully until the urea melts. Continue to 
heat slowly as long as gas is evolved. What is the gas ? Test with 
red litmus paper and by odor. After all ammonia is expelled, cool 
and dissolve in water. Now add to the solution a few drops of very 
dilute CUSO4 solution as described under Experiment XVIII, 4, c. 
The pink color is due to the reaction of the biuret, formed from the 
urea, and the copper sulphate. 

Uric Acid and Purine Bases 

Uric acid is a much more complex compound related to urea. 
It contains two urea residues joined together by a carbon 
nucleus. 

NH-CO 

0C< C-NH V 



>C0 

-TVJTT/ 



NH-C-NH 

Uric acid 

It is what is known as a tautomeric compound, i.e. it exists in 
either of two forms depending upon the conditions and the 
character of the substance acting upon it. The tautomeric 
form is represented by the following formula : 

y N = C-(OH) 

/ I 

(HO)-C C-NH 



N- 



^C-(OH) 

Uric acid 



This is a tri-hydroxy derivative of a hypothetical compound 
known as purine which has the formula, 

/N = CH 

/ I 

HC C-NH^ 

^N-C-N^ 

Purine 



AMINO-ACIDS, PROTEINS, UREA AND URIC ACID 103 

Several well-known and commonly occurring substances have 
been shown to be derivatives of this same hypothetical com- 
pound purine. The simplest of these is xanthine, which is a 
di-hydroxy-purine. It is present in urine and in animal tissues. 
Theobromine, the active constituent of the cocoa bean and pres- 
ent in chocolate and cocoa, is the di-methyl derivative of xan- 
thine, i.e. di-methyl-di-hydroxy- purine. Caffeine, or thein, the 
active constituent of coffee and tea, is a tri-methyl derivative of 
xanthine or tri-methyl-di-hydroxy-purine. Writing the formu- 
las all together will show their relationship. 

/ I 
HC C-NIi 

^N-C-N<^ 

Purine 

^N = C(OH) /NH-CO 

/ I / I 

(HO)C C-NH V or OC C-NH V 

>CH \ II V)H 



^N-C-N^ 



\HN-C-N<^ 

Xanthine, Di-hydroxy-purine 

/N = C(OH) /NH-CO 

/ I / \ 

(HO)C C-NH. or OC C-NH. 

V II J>C(OH) \ || >CO 

Uric acid, Tri-hydroxy-purine 

yNH-CO CH3 

/ I /CH 3 I 

OC C-N< /N-CO /CHa 

\ II >CH / I / 

^N-C-N^ OC C-NC 

I \ II >H 

CH3 \ N _C-N^ 

I 
CH 3 

Theobromine Caffeine 

Di-methyl xanthine Tri-methyl xanthine 



CHAPTER VII 
CARBOHYDRATES 

We come now to the consideration of the third essential 
organic constituent of animal foods, the carbohydrates. The 
other two, viz. fats and proteins, have already been discussed. 
We shall find that the group of compounds known as carbohy- 
drates contains some of the most important substances that have 
to do with plant and animal life and also some which have a 
very great value industrially in other ways than as food. We 
shall confine ourselves now to the study of these compounds 
as to their chemical nature, their classification and relationship 
to each other and their general relation to plants and animals 
and to manufactured products. Their physiological relation to 
plants and animals, their special occurrence in plants and their 
specific industrial uses will be considered later. 

Composition. — The name carbohydrates was originally given 
because it was supposed that they were carbon and water 
compounds. It is now known that they bear no direct relation 
to these two substances other than the fact that they contain 
carbon plus hydrogen and oxygen with these last two elements 
in the same proportion in which they are present in water, 
i.e. H 2 : or two atoms of hydrogen (two parts by mass) to 
one atom of oxygen (sixteen parts by mass). A fact which led 
to the belief that the carbohydrates contain carbon and water, 
is that when they are thoroughly dried and freed from all 
hygroscopic water and also from all water of crystallization and 
then heated out of contact with oxygen they are decomposed 
and water is driven off while carbon remains, 

Carbohydrates + heat — > carbon + water 
This same decomposition occurs when some carbohydrates, 
e.g. cane sugar, are treated with concentrated sulphuric acid 

104 



CARBOHYDRATES 105 

which absorbs water and leaves a residue of pure carbon. The 

general formula for all carbohydrates, with one exception, 

which need not be discussed here, is C n (H 2 0) x . In this formula 

x may have the same value as n or it may be equal to one less 

than n. 

EXPERIMENT STUDY XX 

General Properties of Carbohydrates 

(1) (a) Dry some cane sugar at ioo° C. until all hygroscopic mois- 
ture has been driven off. (b) Heat about a gram of dry cane sugar in 
a test tube. Notice moisture given off as the sugar decomposes. 
What is the residue in the tube ? This proves carbon, hydrogen and 
oxygen as constituents of sugar, (c) To 5 g. of dry cane sugar in a 
test tube add about 5 c.c. concentrated sulphuric acid (c. p.). With- 
out heating notice decomposition due to the removal of water by the 
sulphuric acid and the residue of pure carbon. This is a method of 
preparing chemically pure carbon. 

(2) Make the soda lime test for nitrogen, Experiment XVIH, 2. 
This proves absence of nitrogen. 

(3) Moore's Test. To 5 c.c. of a sugar solution add a little KOH 
and warm. A yellow and then brown color is characteristic of car- 
bohydrates. 

Constitution. Mixed Alcohol-aldehyde or Alcohol-ketone 

Compounds. — Without entering into a detailed discussion 

in regard to the constitution of these compounds, with the 

proofs for each of the views advanced, we may simply state the 

fundamental facts necessary for understanding their relation 

to each other. The simple carbohydrates which are known as 

mono-saccharoses undergo reactions which indicate that they 

contain both alcoholic hydroxyl groups and also an aldehyde or 

ketone group. Furthermore each carbon atom but one has one 

and only one alcoholic hydroxyl joined to it. This remaining 

carbon atom is in the condition of either an aldehyde or ketone 

group. The group characteristic of aldehydes and ketones is 

H R 

I I I 

- C - O, i.e. R - C = O in aldehydes and R - C = O in 

ketones (see p. 42). 



106 ORGANIC AGRICULTURAL CHEMISTRY 

The carbohydrates are also directly related to the poly- 
hydroxy alcohols containing the same number of carbons with 
a hydroxyl joined to each carbon. By the oxidation of these 
polyhydroxy alcohols, with the conversion of one alcoholic group 
only into an aldehyde group or a ketone group, we obtain the 
carbohydrates. 

This will be clear if we illustrate with a concrete example. 
The common sugars glucose and fructose each contain six carbon 
atoms, their formula being C 6 Hi20 6 . They are both related 
to the hexa-hydroxy-hexane which is known as sorbitol and which 
has the constitution as follows : 

OHOHH OH OH OH 

I I I I I I 
H-C-C-C-C-C-C-H Sorbitol 

I I I I I I 
H H OHH H H 

When this is oxidized with the conversion of one of the end 
primary alcohol groups into an aldehyde group, we obtain the 
compound : 

OH H OH OH OH 

II I I I I I 
C-C-C-C-C-C-H Glucose 

I I I I I I 

H H OHH H H 

The compound so obtained is the sugar glucose. When, how- 
ever, the oxidation results in the conversion of one of the sec- 
ondary alcohol groups into a ketone group, we obtain the com- 
pound : 

OH O H OH OH OH 
.1 II I I II 

H-C-C-C-C-C-C-H Fructose 

1 I I I I 

H OH H H H 

This compound is the sugar known as fructose. These two 
formulas agree with the composition of the two sugars, viz. 
CeH^Oe or CeCHaOV The sugars themselves undergo the 



CARBOHYDRATES 107 

distinctive reactions characteristic of aldehydes and ketones, 
viz. they form addition products with hydrogen cyanide, HCN, 
they yield oximes with hydroxyl amine, H 2 N— OH, and 
they form hydrazones when treated with phenyl hydrazine, 
H 2 N— NH— C 6 H 5 . These reactions were referred to in con- 
nection with aldehydes (p. 44) and they have been of the 
greatest importance in the study of the carbohydrates. 

It will not be necessary to discuss these reactions more in 
detail nor to dwell further upon ideas in regard to the constitu- 
tion of the carbohydrates, for these facts are not essential to an 
understanding of their agricultural importance. The more 
important study for us is the occurrence and distribution of 
the carbohydrates in nature, their relation to each other and 
to a few other compounds such as alcohol and lactic acid, and 
their economic uses. Before dismissing the question of consti- 
tution, however, it should be stated that recent work has shown 
that the aldehyde and ketone structure is probably not the form 
in which the carbohydrates actually exist, but that they take 
this form when acted upon by the reagents considered. 

Classification. — The carbohydrates are subdivided into 
several smaller groups, depending both upon the number of 
carbon atoms in the molecule and upon their general com- 
plexity and relation to each other. In the first place there are 
two main groups which are known as simple carbohydrates and 
compound carbohydrates. The simple carbohydrates, or, as they 
are more generally termed, the simple sugars, are known more 
definitely as mono-saccharoses. The name signifies the fact 
that the compounds of this subgroup are the unit sugars. This 
is shown by the fact that they cannot be split or broken down 
by hydrolysis into any simpler units and also because they are 
the unit parts of more complex carbohydrates. The general 
formula is C M (H02) W . Typical examples of monosaccharoses 
are the two common sugars already mentioned, glucose and 
fructose. These both have six carbon atoms in the molecule 
and their formula is, therefore, C 6 (H 2 0)6 or C 6 Hi 2 06. While 
all the monosaccharoses are alike in this unit character, the 



108 ORGANIC AGRICULTURAL CHEMISTRY 

subgroup is further divided into smaller groups depending 
upon the number of carbon atoms in the molecule. The num- 
ber of carbon atoms varies from two to nine and the names 
indicate the number of carbon atoms. Monosaccharoses 
which contain two carbons are called bi-oses and have the 
formula C2H4O2; those containing three carbons are called 
tri-oses with the formula C 3 H 6 3 . Similarly, the other sub- 
groups of monosaccharoses are tetr-oses, C4H8O4, pent-oses, 
C5H10O5, hex-oses, C6H12O6, hept-oses, C7H14O7, oct-oses, C 8 Hi 6 08, 
and non-oses, C 9 Hi 8 9 . Those of special importance and which 
we shall study further are the trioses, pentoses and hexoses. 

The compound carbohydrates are known as poly-saccharoses, 
which signifies that they are made up of more than one unit 
sugar. This is proven by the fact that on hydrolysis they split 
and yield two or more molecules of the monosaccharoses . They 
are further divided into smaller groups according to the number 
of monosaccharose molecules which they yield. Di-saccharoses 
are those polysaccharoses which yield two molecules of mono- 
saccharoses. Their formula is C w (H 2 0) B _i, or C12H22O11, and 
they are typified by the common sugar of commerce, cane 
sugar. Tri-saccharoses are polysaccharoses which yield three 
molecules of monosaccharoses. Their formula is Ci 8 H3 2 0i6 
and an example is the sugar rajfinose. Polysaccharoses, spe- 
cifically so called in distinction from the two subgroups just 
mentioned, are those polysaccharoses which yield an indefinite 
number of molecules of monosaccharoses. This group is 
typified by the common substances, starch and cellulose, with 
the formula (CeHioOs)^. A tabular presentation of the classi- 
fication of carbohydrates will perhaps make the whole matter 
clearer. 



CARBOHYDRATES 



109 



Carbohydrates 



Simple carbohydrates 



I 
Compound carbohydrates 
or 
Polysaccharoses 



Monosaccharoses 



Bioses C2H4O6 
Trioses C 3 H 6 0j 
Tetroses C 4 H 8 04 
Pentoses CsHicOa 
Hexoses CcHizOe 
Heptoses C7H14O7 
Octoses CsHuOs 
Nonoses G>HisO» 



Disaccharoses 
Cane sugar, etc. 

I 
C12H22O11 

I 



I 

Trisaccharoses 

Raffinose, 

Cl8HwOl6 



2 mol. monosacch. 3 mol. monosacch. 



Polysaccharoses 
Starch, Cellulose, etc. 

(OHioOOx 
xmol. monosacch. 



TRIOSES, C 3 H 6 3 

In discussing the constitutional formula for the carbohy- 
drates, as previously given, we showed the relation between 
the six-carbon sugar glucose (a hexose) and the six-carbon hexa- 
hydroxy alcohol sorbitol. The triose sugar bears exactly 
the same relation to the three-carbon tri-hydroxy alcohol which 
we have considered before, viz. glycerol (glycerin). 

OH OH OH 



H-C-C-C-H 

I I I 
H H H 

Glycerol 

O OH OH 



C- C-C-H 

I I I 
H H H 



OH O OH 

I II I 
and H-C-C-C-H 



Glycerose 

The importance of this simple sugar, which is a mixture of 
both the aldehyde and ketone compounds, is that it can be 
made from glycerol and that it undergoes polymerization and 
yields fructose sugar. 



110 ORGANIC AGRICULTURAL CHEMISTRY 

PENTOSES, C 5 H 10 O 5 

The four-carbon monosaccharoses or tetroses are not im- 
portant, but the five-carbon compounds, pentoses, are commonly 
occurring substances in many plants. When certain gums such 
as gum arabic, cherry gum or wood gum, are boiled with acids, 
sugars known as arabinose and xylose are obtained which are 
pentoses, and have the formula C5H10O5. 

These sugars are contained in the gums, not as sugars, but as 
complex compounds which, because they yield pentose sugars, 
are known as pentosans. The substances occur in the woody 
or cellular parts of many plants which are used as animal foods, 
and are directly utilizable by the animal as food nutrients. 
The amount of pentosan compounds in an animal food is, 
therefore, an important item. We shall consider pentosans 
more at length as constituents of plants in Chapter XV, p. 272. 

The one carbohydrate which does not contain the elements 
hydrogen and oxygen in the proportion H 2 : is a pentose 
sugar. It is known as rhamnose and has the composition 
C6H12O5. It is a methyl substitution product of a pentose, i.e. 
(CH 3 )-C 5 H 9 6 . 

EXPERIMENT STUDY XXI 
Pentosans and Pentoses 

(1) (a) Place about 2.0 g. of wheat bran in a flask and boil with 
100 c.c. of dilute HC1 (sp. gr. 1. 15), distilling through a condenser until 
about 25 c.c. of distillate have collected. Now add to the distillate 
some phloroglucinol solution. A green precipitate turning black 
shows the presence of furfural. The furfural has been produced from 
the pentose carbohydrates obtained by hydrolysis of the pentosans 
present in the bran, (b) The same experiment may be performed, 
using gum arabic instead of bran. 

HEXOSES, CeHiaOe 

By far the most important group of monosaccharose sugars 
is that of the hexoses which have six carbon atoms and the for- 
mula C 6 Hi20 6 . The most common members of this group are : 



CARBOHYDRATES III 

Glucose, dextrose or grape sugar, 
Fructose, levulose or fruit sugar, 
Galactose. 

These hexose monosaccharoses all have the formula C 6 Hi2C 6 . 
They differ in constitution in ways that need not be entered 
into here, but we shall consider in detail their relation to the 
polysaccharose carbohydrates. 

We have given to the whole class of simple sugars the name 
of monosaccharoses. This name is given in distinction to those 
of disaccharoses, trisaccharoses and polysaccharoses, and be- 
cause they are the simplest of the entire group of carbohydrates. 
This simple nature is shown by the fact that they do not split up 
by hydrolysis into any simpler carbohydrate compounds. The 
disaccharoses and all polysaccharoses are known as such be- 
cause on hydrolysis they do split up and yield two or more mole- 
cules of these monosaccharoses. 

Glucose or Dextrose, CeH^Oe 

Occurrence and Properties. — The most important and most 
common of the hexose sugars is glucose, also known as dextrose 
and grape sugar because it occurs naturally in ripe grapes. It 
is found also in all other ripe fruits and in honey. It is present 
in small amounts in many plants. It occurs in the blood of 
all animals and in urine in the disease known as Diabetes. As 
we shall find when we study animal nutrition, it is the final form 
into which most of the carbohydrate food is changed in the 
process of digestion, and the form in which it is burned in the 
blood to furnish heat to the animal body. It occurs also in 
combination in plants in the form of complex compounds known 
as glucosides. These glucosides upon hydrolytic decomposition 
yield glucose. An example may be mentioned, viz. amygdalin, 
a glucoside found in bitter almonds and in cherry kernels, which 
by fermentation yields glucose, hydrogen cyanide, and a sub- 
stance known as benzaldehyde, or oil of bitter almonds. 

Determination. — Glucose possesses optical activity as ex- 
plained in connection with lactic acid. It turns the plane of 



112 ORGANIC AGRICULTURAL CHEMISTRY 

polarized light to the right, i.e. it is dextro-rotatory and on this 
account is known also as dextrose. This physical property, 
being constant and definite in amount, is used as a means of 
determining the quantity of glucose in a solution. That is, 
the amount in a solution can be calculated by measuring the 
angle through which it turns the plane of polarized light to the 
right. This will be referred to again when we consider ordinary 
or cane sugar. It is also a strong reducing agent. An am- 
moniacal solution of silver nitrate is reduced to metallic silver 
and an alkaline solution of copper sulphate is reduced to red 
cuprous oxide, Cu 2 0. This last reaction is also used as a 
method of quantitatively determining the amount of glucose in 
solution by weighing the cuprous oxide formed. The copper so- 
lution used in this determination is made up of definite amounts 
of copper sulphate, CuSC>4, potassium sodium tartrate or 
Rochelle salt, KNaC 4 H 4 6 , and sodium hydroxide, NaOH. 
It is known as Fehling's solution, 1 and may be used volume trically 
by titration, as in urine analysis, or gravimetrically by weighing 
the cuprous oxide formed, as is done in the case of ordinary 
solutions containing glucose. Fehling's solution may be used 
in determining the amount of one of the other monosaccharoses, 
viz. fructose, and also the two disaccharoses, malt sugar and 
milk sugar. Glucose is a solid, crystallizing in masses more or 
less wax-like and containing one molecule of water of crystalliza- 
tion. As ordinarily obtained under the name of glucose sirup 
it is a thick, viscous liquid. It is readily soluble in water and 
almost insoluble in absolute alcohol. It tastes only slightly 
sweet. It has numerous industrial applications, in dyeing, in 
the making of confectionery and jellies and in pharmaceutical 
preparations. It is not ordinarily obtained from its natural 
sources, but is made by chemical transformation from other 
members of the carbohydrate group. All three of the common 

1 Allihn's modification of Fehling's solution is made as follows : 
Solution A : CuS04 • 5 H2O, 69.2 g. per litre. 
Solution B : (Rochelle salt, 346 g. +KOH, 250 g.) per litre. 
A and B are mixed in equal volumes and the mixed solution used freshly prepared. 



CARBOHYDRATES 1 13 

disaccharose sugars, viz. cane sugar, malt sugar and milk 
sugar, when acted upon by enzymes or when boiled with acids, 
yield glucose. Starch also by similar reactions is broken down 
into glucose, and this is the commercial method of preparing it. 
These reactions will be more fully considered later. 

Fermentation of Glucose. — By far the most important re- 
action of glucose is its fermentation. When a solution of glu- 
cose is acted upon by the plant organism yeast (saccharomyces), 
it yields alcohol and carbon dioxide. 

CeH^Oe + yeast (zymase) -> 2 C 2 H 5 OH + 2CO2 

This fermentation, as has been fully described under alcohol, 
is due to an enzyme known as zymase, which is secreted by the 
yeast cell. Alcoholic fermentation takes place in all glucose- 
containing solutions whether the glucose is present in such 
solutions naturally, as in grape juice and apple juice, or whether 
it has been formed by a preceding decomposition of malt sugar 
or starch, as in the case of malted grain. 

Fructose or Levulose, CeH^Os 

Fructose or levulose is also known as fruit sugar, and is found 
usually associated with glucose in fruits such as grapes, and in 
honey. As its name, levulose, signifies, it is oppositely active 
toward polarized light to dextrose, being lew-rotatory. It 
does not crystallize easily, being more soluble than glucose both 
in water and in alcohol. It is like glucose in fermenting with 
yeast zymase, though less rapidly, and in reducing Fehling's 
solution. In their constitution glucose and fructose differ in 
that the former is an aldehyde-alcohol compound and the latter 
a ketone-alcohol compound. In the decomposition of cane 
sugar by enzymes or by boiling with acids not only glucose but 
also fructose is formed, and in equal molecular amounts, one 
molecule of glucose and one of fructose. In the decomposition 
of starch and malt sugar, however, only glucose is formed. 
Fructose is the direct product of a laboratory synthesis of sugars. 
Formaldehyde when treated with alkali is converted into this 



114 ORGANIC AGRICULTURAL CHEMISTRY 

sugar. Also the three-carbon sugar glycerose, which may be 
made from glycerol, condenses and yields fructose. As fructose 
may be converted into glucose, we may say that both of the 
hexose monosaccharoses have been synthesized in the labora- 
tory. There is pretty general belief that this formaldehyde 
synthesis of glucose and fructose represents part of the process 
by which carbohydrates are photo-synthesized in green plants. 

Galactose, CeHi 2 06 

Galactose, the third monosaccharose hexose sugar, may be 
simply mentioned. It is obtained together with glucose when 
milk sugar is hydrolyzed by enzymes or acids. It is dextro- 
rotatory and ferments with yeast zymase. It has not been found 
free in either plants or animals, but occurs in combination in 
certain glucosides, especially one known as cerebron found in the 
brain. In plants it occurs also as polysaccharose derivatives 
known as galactans. These latter will be referred to again. 



EXPERIMENT STUDY XXII 

Hexoses 

(i) Examine for general properties, such as solubility in water and 
in alcohol, taste, etc., (a) Glucose or dextrose; (b) Fructose or levu- 
lose. 

(2) To 5 c.c. Fehling's solution add about 1 c.c. of glucose solution. 
Warm. Notice reduction of the copper sulphate to red Cu 2 0. Allow 
to settle. If a blue color remains, add a little more sugar solution 
and repeat until all copper sulphate has been reduced. 

(3) Repeat the Fehling's solution test with a solution of levulose. 

(4) Perform Experiment XX, 3, with both glucose and fructose. 

(5) To 5 c.c. of ammoniacal silver nitrate solution add a little glu- 
cose solution and warm in hot water. Notice formation of silver 
mirror due to the reduction of the silver solution. 

(6) Make up a 1.0 per cent solution of glucose. Mix this solution 
with 1.0 g. yeast and fill a Fermentation tube with the mixture. Allow 
to stand 24 hours, and determine the amount of C0 2 evolved. This 
fermentation tube is a form of clinical apparatus known as a Sac- 



CARBOHYDRATES 115 

charometer. It is so graduated as to read directly, from the volume 
of C0 2 , the per cent sugar in the original solution. The calculation 
is based on the following reaction : 

C6H 12 6 -> 2 C0 2 + 2 C 2 H s OH 

180 88 

(7) Ferment glucose on a larger scale and obtain the alcohol as a 
distillation product. (See Experiment VIII.) 



DISACCHAROSES, C12H22O11 

The disaccharoses are sucrose or cane sugar, maltose or malt 

sugar and lactose or milk sugar. All of these compounds split 

by hydrolysis when acted upon by enzymes or when boiled with 

acids and yield two molecules of monosaccharoses, hence their 

name, disaccharoses. They possess the composition C12H22O11 

and the reaction by which they split up into monosaccharoses 

is as follows : 

Ci 2 H 22 0n+ H 2 -^ 2 CeH^Oe 

Disaccharose Mono- 

saccharose 

The disaccharoses may thus be considered as anhydrides of 
two molecules of monosaccharoses. The conversion of di- 
saccharoses into monosaccharoses, involving simply the addi- 
tion of a molecule of water, is termed a reaction of hydrolysis. 
We thus speak of hydrolyzing disaccharoses to monosaccharoses. 
This hydrolysis, as has been stated, takes place either through 
the agency of chemical substances known as enzymes or when the 
disaccharoses are boiled with dilute acids. 

Sucrose or Cane Sugar, Ci2H 22 0n 

Occurrence. — The most important of the disaccharoses is 
sucrose, or as it is known because of its most important source, 
cane sugar. It is very widely distributed in nature and occurs 
in almost all plants in greater or less amounts. The two most 
abundant sources from which it is obtained are the sugar cane, 
from which it derives its name of cane sugar, and the beet, in 



Il6 ORGANIC AGRICULTURAL CHEMISTRY 

which it occurs in exactly the same form as in the sugar cane. 
It is also found in considerable amount in sorghum cane and in 
the sap of maple trees, especially the hard or sugar maple {Acer 
saccharum). Other rather abundant sources are vegetables 
such as carrots, parsnips, artichokes, in such fruits as strawberries 
and pineapples, in the sap of some other trees such as beech, and 
in some nuts such as chestnuts. 

Properties. — Cane sugar is a crystalline solid, forming 
monoclinic prisms. It is easily soluble in water and slightly 
so in alcohol. It melts at 160 C, and when melted and allowed 
to cool it forms a transparent vitreous-like mass known as 
barley sugar, which gradually becomes crystalline. When heated 
to 2io° C, it loses water and is converted into a brown amorphous 
mass known as caramel which is used as a brown coloring agent, 
and as a flavoring substance of a characteristic taste. Heated 
still higher it decomposes, yielding finally a residue of carbon 
and giving off water and a mixture of volatile products contain- 
ing several hydrocarbons, aldehydes and acids. When sugar 
is treated with concentrated sulphuric acid, it is decomposed with 
the evolution of heat and a residue of carbon is left. (See 
Experiment XX, i, c.) If this is washed to remove the acid, 
pure carbon is obtained, and this is used as a method of making 
pure carbon. Cane sugar is dextro-rotatory, but it does not 
reduce Fehling's solution. When pure cane sugar is treated 
with Fehling's solution, reduction often occurs after some 
minutes' boiling, because the sugar is first hydrolyzed into 
glucose and fructose which then reduce the Fehling's solu- 
tion. 

Cane sugar does not undergo alcoholic fermentation by the 
action of the enzyme zymase as do glucose and fructose. Yeast 
contains not only the alcoholic enzyme zymase but also enzymes 
which hydrolyze cane sugar and the other disaccharoses. When, 
therefore, cane sugar is subjected to yeast fermentation, alcohol 
is produced, due to a double process. First the cane sugar is 
hydrolyzed by the yeast enzyme sucrase or invertase and con- 
verted into glucose and fructose. These monosaccharoses are 



CARBOHYDRATES 1 17 

then fermented by the alcohol producing enzyme zymase, and 
alcohol results, 

C12H22O11 + sucrase + H 2 -> 2 CeH^Oe 

Cane sugar Glucose and 

Fructose 

C 6 Hi 2 6 + zymase -> 2 C 2 H 5 OH + 2 C0 2 

Glucose and Fructose Alcohol 

Hydrolysis. — When sucrose is hydrolyzed by enzymes or 
by boiling with acids, it yields two molecules of monosaccharoses. 
One molecule, however, is dextro-rotatory glucose and the other 
is lew-rotatory fructose. 

C12H22O11 + H 2 — > C6H12O6 + C6H12O6 

Cane sugar Glucose Fructose 

Inversion. — As fructose is more strongly levo-rotatory 
than glucose is dextro-rotatory, a mixture of equal molecules of 
each is not inactive like equal molecules of dextro and levo 
lactic acid or tartaric acid, but is levo-rotatory. As the su- 
crose itself is dextro-rotatory, the hydrolysis thus changes or 
inverts the solution as to the direction in which it rotates the 
plane of polarized light. The process of converting sucrose into 
a mixture of glucose and fructose is, therefore, known as inver- 
sion t and the mixture of glucose and fructose obtained is called 
invert sugar. Invert sugar then is the mixture of equal mole- 
cules of glucose and fructose obtained by the hydrolysis or 
inversion of sucrose. 



C12H22011 -f- H20 — > C6H1206 


-f- C6H12O6 


Sucrose Hydrolysis Glucose 


Fructose 


Dextro- or Dextro- 


Levo- 


rotatory Inversion rotatory 


rotatory 



Invert sugar, levo-rotatory 

The similar hydrolysis of the other disaccharoses, maltose 
and lactose, yields products of the same direction of optical 
rotation. These hydrolyses do not, therefore, result in inver- 
sion. 

Invert Sugar. — Invert sugar may be separated by crystal- 
lization into the more readily crystallized glucose and the less 



Ii8 ORGANIC AGRICULTURAL CHEMISTRY 

readily crystallized fructose, but the crystallization is difficult 
and it is not a practical method for obtaining glucose. Invert 
sugar occurs in honey together with sucrose. As both glucose 
and fructose reduce Fehling's solution, invert sugar also re- 
duces it and in a definite amount. The determination of the 
amount of sucrose in a solution by inverting it and then deter- 
mining by Fehling's solution the amount of invert sugar present 
is a practical laboratory method of analysis. As sucrose is 
dextro-rotatory and invert sugar is levo-rotatory the deter- 
mination of the optical rotation both before and after inver- 
sion gives a second practical method for determining the amounts 
of sucrose and invert sugar present in a mixture of the two sub- 
stances. 

Sugar Analysis. — This is in brief the principle of methods of 
analysis of all sugar-containing liquids such as are dealt with 
in all sugar-producing and refining processes, or in the study 
of plant constituents. Details of methods will be found in books 
on analytical chemistry or sugar analysis. 

Maltose, Malt Sugar, C12H22O11 

Maltose or malt sugar is the second of the important di- 
saccharoses. It is present in malted grain, or malt, where it is 
produced from starch. When malt is extracted with water 
and the extract evaporated, a sirup is obtained containing 
maltose in solution. From such solution maltose may be ob- 
tained as a crystalline substance. It forms needle crystals 
with one molecule of water. It is easily soluble in water, and 
only slightly so in alcohol. It reduces Fehling's solution, but 
is not fermentable by zymase. It is optically active, being dextro- 
rotatory. After hydrolysis to a monosaccharose, as in the case 
of cane sugar, the product is fermentable. When hydrolyzed 
by enzymes or by boiling with acids, two molecules of glucose are 
obtained. This reaction is not accompanied with optical in- 
version as in the case of cane sugar, as both the maltose and the 
hydrolytic product, glucose, are dextro-rotatory. 



CARBOHYDRATES 119 

Lactose, Milk Sugar, C12H22O11 

Lactose or milk sugar. — The third disaccharose, as its name 
signifies, is found in the milk of mammals. It is not found in 
any plants. In milk, it is present to the extent of about 4-5 
per cent. When both the fat and the protein have been sep- 
arated from the milk, the remaining liquid on evaporation yields 
lactose (see Experiment XXIX) . This separates as a crystalline 
substance, often in large crystal masses resembling cane sugar 
crystals or rock candy. The crystals contain one molecule of 
water. It also crystallizes with three molecules of water. It 
is soluble in six parts of water, and is slightly sweet. Like 
maltose, lactose reduces Fehling's solution, and both of these 
sugars may be determined quantitatively by means of this 
reagent, as in the case of glucose and fructose. It is optically 
active, being dextro-rotatory. When hydrolyzed by enzymes or 
boiling acids it yields one molecule of glucose and one of galactose, 
both being also dextro-rotatory so that no inversion takes place. 
It is not fermented by zymase. With yeast alcoholic fermenta- 
tion occurs slowly after the lactose is first hydrolyzed by another 
enzyme of the yeast, probably lactase. 

Lactose differs from the other two disaccharoses in readily 
undergoing a bacterial fermentation' by which lactic acid is 
produced. As explained in connection with lactic acid, lactose 
is fermented by the lactic acid bacteria and inactive lactic acid, 
or fermentation lactic acid, is obtained. These bacteria are 
naturally present in milk, and after standing fermentation 
takes place, the lactic acid is formed and the milk, as we say, 
sours. The chemical reaction in the conversion of lactose into 
lactic acid is first one of hydrolysis into glucose and galactose, 
and then one of simplifying the molecule without hydrolysis, 
oxidation or any other chemical reaction. 

C12H22O11 + H 2 -> 2 C 6 Hi20 6 

Lactose Glucose and 

Galactose 

C 6 Hi20 6 -> 2 C 3 H 6 3 

Glucose Lactic acid 



120 ORGANIC AGRICULTURAL CHEMISTRY 

EXPERIMENT STUDY XXIII 

Disaccharoses 

(i) Sucrose or Cane Sugar, (a) Test a 10 per cent cane sugar 
solution with Fehling's solution as in Experiment XXII, 2. (b) To 
5 c.c. of sugar solution, add 1.0 c.c. of dilute (1 : 1) HC1, boil for 5 
minutes. Neutralize excess of acid with Na 2 C03 and then test with 
Fehling's solution, (c) Heat a little cane" sugar carefully in a test 
tube. Notice darkening in color and characteristic odor (caramel). 

(2) Repeat (1, a) and XX, 3 with maltose (malt sugar). 

(3) Repeat (1, a) and XX, 3 with lactose (milk sugar). 

POLYSACCHAROSES (NOT SUGARS), (CbHkA)* 

The polysaccharoses, or more strictly speaking those poly- 
saccharoses not sugars, for the disaccharoses are of course poly- 
saccharoses, include the common and very widely distributed 
substances, starch, dextrin, cellulose, and the less common glyco- 
gen found in animals. 

Hydrolysis. — The formula for the polysaccharoses is 
(C 6 Hi O5) x . The size of the molecule is unknown, but it is 
probably quite large. Like the disaccharoses these polysac- 
charoses are hydrolyzed by enzymes, and by boiling with acid. 
They each yield the monosaccharose glucose. 

This hydrolysis of polysaccharoses to monosaccharoses is 
connected with several very important processes both natural 
and industrial. The natural processes occur in both plants and 
animals. In the green leaves of plants the carbohydrate, starch, 
which has been built up by the photosynthetic action of the 
leaves is converted by means of the enzyme diastase into maltose, 
and then by maltase enzyme into glucose. In all starch-con- 
taining seeds, when germination begins, the starch is converted 
by the same enzymes into these products. This process when 
produced artificially is known as malting, and the germinated 
seed or grain containing both glucose and maltose sugars is known 
as malt. By a completion of the enzyme action by means of 
zymase alcoholic fermentation takes place and the glucose 



CARBOHYDRATES 121 

formed yields alcohol. This, as has been discussed under al- 
cohol, is the source of most of the industrial alcohol and of the 
alcohol in both malt and distilled beverages. 

In the animal body two hydrolytic conversions of polysac- 
charoses occur. First, the digestive process by which starch 
food is hydrolyzed by the enzyme ptyalin, found in the saliva, 
and converted into maltose sugar. This is then further hy- 
drolyzed by the enzyme maltase, found in the saliva and also 
in the intestinal juice, and yields glucose. Second, the meta- 
bolic conversion of glycogen in the liver and in the muscle cells 
into glucose also probably by enzyme action. 

Source of Alcohol. — The industrial processes by which 
polysaccharoses are hydrolyzed to monosaccharoses, in addi- 
tion to the natural process of malting grain already referred to, 
are : First, the hydrolysis of starch by means of boiling dilute 
acid into glucose for the purpose of obtaining the sugar or 
sirup known as glucose. Second, the hydrolysis of cellulose 
by means of acid to obtain glucose which by alcoholic fermen- 
tation then yields alcohol. This process of obtaining alcohol 
from cellulose material is being developed at the present time 
as a means of securing cheap alcohol for industrial purposes. 
All of these processes of hydrolyzing the polysaccharoses will 
be considered in detail later in this study in connection with 
the plants and animals concerned. 

Starch, (CgHkA)* 

Occurrence and Properties. — Starch is a constituent of some 
part of practically all plants. It occurs in especially large 
amounts in such plants as potato tubers, wheat, corn and other 
cereal grains, arrowroot, certain palms (sago), cassava, etc. 
In its general properties and relation to water, starch belongs 
to the class of bodies known as colloids. It does not dissolve 
in water, but may be so mixed with it as to remain suspended 
indefinitely in the form of an emulsion. In such form it is 
known as starch paste. It is non-diffusible through a semi- 
permeable membrane. When dry, starch is a fine powder and 



122 ORGANIC AGRICULTURAL CHEMISTRY 

is composed of small pieces or grains. These grains possess a 
definite microscopical structure which is different for the starch 
obtained from different plants. This makes possible the iden- 
tification of starches as to their source, and is used in detecting 
adulteration of starches or starch-containing materials. When 
placed in cold water these starch grains remain unbroken and 
the starch does not mix with the water, but settles out on 
standing. If, however, the starch is boiled in water the grains 
are ruptured and the contents then mix with the water as an 
emulsion or colloidal suspension known as starch paste. In 
this form starch is adhesive, and is used as a substitute for 
gums and in sizing cloth and paper. When starch is brought 
in contact with a solution of iodine, a blue compound is formed. 
This blue color of iodine and starch is used in a number of ways 
as a test for starch or for free iodine. Starch grains treated 
with iodine take on a beautiful blue color under the micro- 
scope. The structure of the grains is shown very clearly so that 
starch grains and other similar granular substances are readily 
distinguished. Paper moistened with a starch paste to which 
potassium iodide has been added turns blue as soon as any io- 
dine is liberated from the potassium iodide. This paper is thus 
a test for ozone, hydrogen peroxide, nitrous oxide or any other 
oxidizing substance which will set iodine free from its iodide 
salts. When starch is hydrolyzed by enzymes or by boiling 
with acids, a test with iodine solution readily indicates when 
all starch has been hydrolyzed. Starch does not reduce 
Fehling's solution, is non-fermentable by zymase and is inactive 
optically. 

Hydrolysis. — When hydrolyzed by acids or enzymes, starch 
yields glucose only. In the enzymatic hydrolysis, two enzymes 
are chiefly concerned. In plants, both in green leaves and in 
seeds, the enzyme diastase converts starch into maltose sugar. 
In the animal body the saliva contains the enzyme ptyalin and 
the pancreatic juice contains the enzyme amylopsin both of 
which similarly hydrolyze starch into maltose. Associated 
with diastase in plants and with ptyalin in saliva and also pres- 



CARBOHYDRATES 12 $ 

ent in the intestinal juice is another enzyme maltase which 
hydrolyzes maltose into glucose. This enzyme is also present 
in yeast. The complete enzymatic hydrolysis of starch there- 
fore yields glucose as the final product. In the acid hydrolysis 
of starch glucose is also the final product, the intermediate 
products being probably the same as in the case of enzymatic 
hydrolysis. 

Source of Glucose. — The acid hydrolysis of starch is em- 
ployed in the manufacture of commercial glucose from starch. 
The starch is boiled with dilute sulphuric acid until a test with 
iodine for starch and with Fehling's solution for glucose shows 
that all starch has been converted into the sugar. The excess 
of sulphuric acid is then removed by precipitation and the 
sugar-containing filtrate is evaporated to a thick sirup known 
as glucose sirup (Karo Corn Sirup). In making Karo Corn 
Sirup the hydrolysis is not carried to completion, a good deal 
of maltose and dextrin being present which prevents the crys- 
tallization of the sirup. By complete hydrolysis and subse- 
quent evaporation the glucose sugar crystallizes out as a solid. 
Glucose so obtained is a commercial product used as described 
under glucose sugar. 

Determination. — Starch may be determined quantitatively 
by converting it into glucose either by means of diastase and 
maltase, by boiling with acids or by heating with steam under 
pressure. The resulting glucose is then determined by means 
of Fehling's solution or by its optical rotation. 

EXPERIMENT STUDY XXIV 

Starch 

(i) Test corn, potato and wheat or rice starch for general char- 
acter, and under the microscope for shape of starch grains. While 
under microscope add a drop of iodine solution. 

(2) Test solubility of starch (any variety) in cold water. 

(3) Mix a little starch (2.0 g.) with cold water to make a thin paste. 
Heat a liter of water to boiling. While boiling add the cold starch 



124 ORGANIC AGRICULTURAL CHEMISTRY 

mixture and continue to boil a few minutes. This is a colloidal sus- 
pension of starch and is known as starch paste. 

(4) Test this starch paste solution with iodine solution. Dilute 
the starch paste 10, 100 and 1000 times, and test each with iodine 
solution. 

(5) Dilute 5 c.c. starch paste, with 100 c.c. water, add 5 c.c. of con- 
centrated HC1 and boil for 10 to 15 minutes. Neutralize excess acid 
with Na 2 C0 3 and test a little with iodine solution, and another por- 
tion with Fehling's solution. The starch is hydrolyzed by boiling 
with acids as follows : 

(C6HiA),+ x H 2 -> x C 6 H 12 6 

Starch Glucose 

Dextrin 

When starch is hydrolyzed by diastase or ptyalin, and also 
probably by acids, dextrin is formed as an intermediate prod- 
uct between starch and maltose. Dextrin is soluble in cold 
water, forming a sirup with adhesive properties, and is used 
commercially in several ways. It is optically active, being dextro- 
rotatory, and reduces Fehling's solution. It is non-fermentable 
with zymase. Toward iodine, dextrin acts in different ways 
indicating the existence of several varieties. One form, known 
as erythro-dextrin, is colored reddish brown with iodine. An- 
other form known as achroo-dextrin is colorless with iodine. 
Achroo-dextrin is also known in three varieties called a-, /?- and 
y-achroo-dextrin. All of these varieties of dextrin have been 
proven as intermediate between starch and maltose in the 
enzymatic hydrolysis of starch. 

Glycogen 

Glycogen is known as animal starch. It resembles starch 
and is found in the animal body. It is present in the liver and 
in the muscle cells as a reserve form of carbohydrate food 
material. It is broken down in the body, yielding glucose. 
This will be considered further in connection with animal 
metabolism. 



CARBOHYDRATES 1 25 

Inulin 

Inulin is another starch-like carbohydrate found in certain 
plants, e.g. in potatoes, dandelion roots and dahlia tubers. 
On hydrolysis inulin is converted into fructose alone and not 
glucose. 

Cellulose 

Cellulose is one of the most important carbohydrates, con- 
sidering its wide distribution in nature and the useful prod- 
ucts made from it. The other two most important carbo- 
hydrates considered in this same way are cane sugar and starch. 
Cellulose is as widely distributed in nature as starch, and is the 
chief constituent of the fibrous portions of all plants. The 
fiber of cotton, flax and hemp plants is nearly pure cellulose 
and yields the materials known as cotton, linen and hemp, 
from which important products are made in the shape of cot- 
ton wool, thread or cloth, linen thread or cloth, and hempen 
twine and rope. It occurs also as the fibrous constituent of 
the straw of cereal grains and grasses, and in trees. 

In woody fibers of the latter cellulose is not pure, but is 
present together with (probably in combination with) other 
substances known as lignin, cutin, etc., the compounds being 
termed ligno-celluloses in the first case and adipo-celluloses in 
the latter. In juicy fruits and also in the stems and roots of 
plants the cellulose or fibrous part contains similarly com- 
pounds of cellulose with another group of substances known as 
pectins, the compounds being termed pecto-celluloses . When 
fruit juices form jellies, it is due to the decomposition of these 
pecto-celluloses and the gelatinization of the pectins resulting. 

Cellulose, like starch and unlike sugars, is insoluble in water, 
and unlike starch does not go into solution or colloidal suspen- 
sion on boiling. When heated with dilute sulphuric acid, cellu- 
lose is converted into a starch-like substance called amyloid 
which gives the starch blue test with iodine. When this is 
boiled with acid it is hydrolyzed to glucose. Thus cellulose may 
be converted into glucose which may later be fermented to alco- 



126 ORGANIC AGRICULTURAL CHEMISTRY 

hoi. This production of alcohol from cellulose is in the experi- 
mental stage, as the process has not yet been perfected so as to 
be generally profitable on the commercial scale. Starch is still 
the chief source for the manufacture of alcohol. When unsized 
paper (filter paper) is treated with concentrated sulphuric acid 
for a short time and the acid then removed by washing with 
water, the paper is changed into a tough membrane-like form, 
which is known as parchment paper. 

Cellulose is insoluble in dilute acids or alkalies, and the 
fibrous part of plant food not dissolved by such treatment is 
largely cellulose and is termed in analysis of foodstuffs crude 
fiber. Such crude fiber or cellulose is largely indigestible, pos- 
sessing a coefficient of digestibility in domestic animals of only 
about 30 to 60 per cent. The purest form of cellulose readily 
obtainable is made from cotton fiber or filter paper by washing 
in alcohol, ether and dilute acids and alkalies. A reagent which 
dissolves cellulose is the so-called Schweitzer's reagent, which 
consists of copper hydroxide dissolved in ammonia. 

Paper. — Paper in its various forms or grades consists of more 
or less pure cellulose. The source of the cellulose for the manu- 
facture of paper may be the straw of cereals or grasses, cotton 
fiber either as such or as worn-out cotton cloth, the fiber of such 
soft woods as spruce or pine, and linen, which is the cellulose 
fiber of flax. Such material is first shredded and then treated 
with solvents such as alcohol, ether and dilute alkalies and 
acids, in order to remove all oils, gums and other soluble constit- 
uents. The fibrous pulp thus obtained is then passed through 
rolls and dried in the form of thin sheets. The material is 
bleached to remove all coloring matter, and is sized with rosin, 
to give it a smooth surface. The purity of the product and the 
fineness of its texture depend upon the thoroughness of the 
treatment. The strength and durability depend upon the 
physical character of the fiber used. Linen papers are stronger 
and are more durable than those made from cotton or wood. 
The fine filter paper used in chemical laboratories is practically 
pure cellulose. 



CARBOHYDRATES 1 27 

Mercerized Cotton and Artificial Silk. — When ordinary 
cotton is treated with moderately strong alkalies, compounds 
are formed with the cellulose which decompose again with 
water, yielding hydrates of cellulose. The cotton so treated 
maintains its general character, but is more or less transparent, 
resembling silk in appearance and possesses greater strength 
than the original cotton. It can also be dyed more readily 
than the original cotton. Such a product is known as mer- 
cerized cotton. This is not, however, what is known as artificial 
silk. The latter is prepared from cellulose by various methods. 
A solution of cellulose in Schweitzer's reagent or a solution of 
certain derivatives, e.g. nitrates or acetates, is passed through 
capillary tubes into a liquid which reprecipitates the cellulose 
or its derivatives. It is thus obtained in the form of fine threads 
or fibers consisting of pure cellulose or some derivative of it. 
As it is thus obtained it possesses many of the characters 
of silk and is commercially used as artificial silk. It can be 
readily dyed, possesses considerable silky luster, but though 
more durable and stronger than cotton or other cellulose fibers 
is not as strong or as durable as pure silk. 

Explosives and Celluloid. — The chemical derivatives of cel- 
lulose are chiefly of two classes, viz. nitrates and acetates. 
These have been referred to as having been used in the prepa- 
ration of artificial silk. The nitrates of cellulose are, however, 
a very important class of derivatives in themselves. When 
treated with nitric acid cellulose forms derivatives containing 
two to six nitric acid groups. When a mixture of nitric and 
sulphuric acid is used, six nitric acid groups unite with the 
cellulose and the compound, cellulose hexanitrate, is formed. 
This compound is highly explosive and is the chief constituent 
of gun cotton. Gun cotton explodes violently when struck or 
when set off by means of a detonator, but will burn quietly when it 
is ignited. It is used as an explosive by itself or mixed with nitro- 
glycerin. It is also a constituent of some smokeless powders. 

When cellulose is treated with nitric acid in a less concentrated 
form or for a shorter time, the nitrates of cellulose containing 



128 ORGANIC AGRICULTURAL CHEMISTRY 

two, three, four and five nitric acid groups are formed. A 
mixture of these lower nitrates of cellulose is called pyroxylin 
or soluble gun cotton. It is soluble in alcohol and ether. Such 
an alcohol-ether solution of pyroxylin is known as collodion and 
is used in photography. When pyroxylin is mixed with camphor 
and heated, a plastic mass is obtained which can be molded into 
various shapes. This is known as celluloid. It is inflammable, 
but non-explosive, and is used in manufacturing a great variety 
of small articles for ornamental and toilet purposes. 



EXPERIMENT STUDY XXV 

Cellulose 

(i) Examine some cotton fiber and some filter paper as examples 
of practically pure cellulose. 

(2) Test solubility of cellulose in ordinary reagents and in Schweit- 
zer's reagent prepared as follows : To a solution of copper sulphate 
add sodium hydroxide until a heavy light blue precipitate is formed. 
(Excess of the alkali will dissolve the precipitated cupric hydroxide 
to a deep blue solution.) Filter the cupric hydroxide, and wash out 
all excess alkali. To 10 or 15 c.c. of concentrated ammonium 
hydroxide add the cupric hydroxide as long as it will dissolve in the 
ammonia. The deep blue solution resulting is ammoniacal cupric 
oxide, and is known as Schweitzer's reagent. 

(3) Parchment Paper. Dip a piece of filter paper into dilute sul- 
phuric acid i :• 1. Remove the paper immediately and rinse in run- 
ning water until well washed. The paper will be found to be tough 
and transparent and gives a blue test with iodine. It is called parch- 
ment paper. 

(4) Hydrolysis of Cellulose to Glucose. Shred up a little filter 
paper and add it to 10 c.c. concentrated sulphuric acid. Allow to 
stand until the paper is all dissolved. When all dissolved, pour the 
acid solution into 200 c.c. of water. Test a little of the dilute solu- 
tion with iodine solution. What does the test show? The product 
is known as amyloid from amylum which is starch. Now boil the 
dilute solution for a half hour or so, and test a little with iodine, and 
another portion with Fehling's solution. What does the test show ? 



CARBOHYDRATES 



129 



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130 ORGANIC AGRICULTURAL CHEMISTRY 

The reaction is the same as that for the hydrolysis of starch, Experi- 
ment XXIV, 5. 

Summary of the Carbohydrates. — The importance of the 
carbohydrates may be emphasized by briefly reviewing them. 
In this class we have the important food materials, starch, cane 
sugar, malt sugar, milk sugar, glucose and fructose. Starch is 
also widely used industrially as a sizing material and in the 
manufacture of alcohol and glucose. Dextrin is used as an ad- 
hesive. Cellulose has the greatest use industrially. It is the 
constituent of such useful materials as cotton, linen, hemp, 
jute and paper in all their various forms. Derivatives of cellulose 
or cellulose that has been modified in form by certain treatment 
are important as explosives (gun cotton, etc.), collodion, cellu- 
loid, mercerized cotton and artificial silk. Also glucose and 
glycogen are important metabolic products of the animal 
body. When we add to all this the fact that the carbohydrates 
are most widely and abundantly distributed in plants, we 
realize their extreme importance in relation to agriculture. 

UNSATURATED COMPOUNDS 

While the carbohydrates are the last group of compounds of 
any direct importance in our present study there still remains 
an entirely distinct class of compounds which we shall briefly 
mention. 

In the compounds which we have discussed we have con- 
sidered representatives of all of the characteristic divisions or 
groups, as follows : 

Hydrocarbons; simple substitution products of the hydro- 
carbons such as mono- and poly-halogen products, and amino 
compounds, mono- and poly-hydroxy compounds or alcohols, 
glycerol, etc. ; aldehydes ; ketones ; mono- and poly-carboxy 
acids; esters or ethereal salts, including the glycerol esters or 
fats ; amides such as urea ; the related uric acid or purine com- 
pounds ; hydroxy-acids ; amino-acids and the related proteins ; 
hydroxy-aldehydes and the related carbohydrates. 



CARBOHYDRATES 131 

In the new class of compounds which we shall consider we 
shall meet with no new group of derivatives but mention a few 
which, though of like character, are derived from other hydro- 
carbons which possess a distinctly new property and constitu- 
tion. 

All of the compounds thus far considered have been derived 
from members of the methane or saturated series of hydro- 
carbons. In this series one of the fundamental ideas in con- 
nection with them is that of saturation. In methane and all of 
its derivatives the carbon atoms are always fully satisfied or 
are saturated, and this is shown by the fact that so far as the 
carbon atoms are related to each other they are united by only 
a single linkage and furthermore whenever derivatives are 
formed it is by a reaction of substitution, never by addition of 
new elements or groups. Each carbon element has four uni- 
valent elements or groups attached to it as in ethane, H3C-CH3 
or ethyl alcohol H3C— CH 2 (OH) or one bivalent element and 
two univalent elements or groups as in aldehydes, 

R-C=0 R-C=0 

and in acids 
H OH 

or the carbon has a trivalent element and one univalent element 
or group as in the cyanides R — C=N. In some cases ad- 
dition does occur due to the conversion of a bivalent oxygen 
into a univalent hydroxyl, necessitating the addition of a new 
univalent group as in the addition products of the aldehydes. 

NH 2 

I 
R-C = 0+HNH 2 -> R-C -OH 

A k 

Aldehyde Aldehyde ammonia 

But in none of these cases of addition does the change effect 
the single linkage by which carbons are united to each other. 
Unlike these saturated hydrocarbons we have other hydro- 



132 ORGANIC AGRICULTURAL. CHEMISTRY 

carbons which readily take up elements by addition to the mole- 
cule in such a manner as to indicate that in them the carbon 
atoms are not fully saturated. Ethylene or ethene gas, the 
simplest member of the series, has the composition C2H4 and 
when treated with bromine it easily takes up two atoms as 

follows : 

C2H4+ Br 2 ->C 2 H 4 Br 2 

Ethylene Ethylene bromide 

The compound formed is known as ethylene bromide and also as 
symmetrical di-brom-ethane. It is the same compound as is 
obtained from ethane gas, C 2 H 6 , by substituting two bromine 
atoms for two hydrogens. This latter reaction, as discussed 
previously (p. 20), we represent as follows: 

H H H H 



c- 

1 


-c- 

1 


H + 


2Br 2 -> Br- 


-C- 

1 


-C- 

1 


-Br + 


2 HBr 


1 
H 


1 
H 






1 
H 


H 






Ethane 




Di-brom-ethane (symmetrical) 





As this same product is obtained by adding two bromine atoms 
to ethylene we are led to represent the reaction and the con- 
stitution of ethylene as follows : 

H H H H 

II II 

C = C +Br 2 ->Br-C-C-Br 

I I I I 

H H H H 

Ethylene Di-brom-ethane, or 

Ethylene bromide 

In ethylene we believe that the two carbons are only partly 
saturated, each one having one free valence or bond, but that 
this bond instead of remaining free is joined to the other carbon, 
thereby making the two carbon atoms doubly joined, instead of 
singly, as in the methane hydrocarbons. This double linkage 
of two carbon atoms is not a point of strength, but rather of 
weakness due to strain, and thus is easily broken and converted 
into singly bound carbons while the broken bond of each carbon 



CARBOHYDRATES 



133 



atom becomes satisfied with the added bromine. In exactly 
a similar way we have compounds in which the carbon is con- 
sidered as triply linked with another carbon atom while only 
the remaining bond is held by another element or group. Such 
a hydrocarbon is the common illuminating gas, acetylene, C2H2, 
and is represented as HC=CH. 

Now similar to each of these hydrocarbons we have an ho- 
mologous series of higher hydrocarbons related to the simplest or 
mother substance just as ethane and the higher paraffin hydro- 
carbons are related to methane. These two series are known 
as the ethylene series and the acetylene series. Their relation 
to each other and to the methane series is readily seen if they 
are placed together as represented by their structural formulas. 



Saturated Hydrocarbons 


Unsaturated Hydrocarbons 


Methane Series 


Ethylene Series 


Acetylene Series 


Methane, H-CH3 
Ethane, H3C-CH3 
Propane, H 8 C-CH 2 -CH3 
Butane, 

H3C-CH2-CH2-CH3 


Ethylene, H 2 C=CH 2 
Propylene, H 3 C-CH=CH 2 
Bulylene, 

H 3 C-CH 2 -CH=CH 2 
or H 3 C-CH=CH-CH 3 


Acetylene, HC=CH 
Allylene, H 3 C-GeCH 
Ethyl acetylene, 
H3C-CH 2 -C=CH 



Each of these unsaturated series, viz. the ethylene hydro- 
carbons and the acetylene hydrocarbons, form derivatives, 
such as alcohols, aldehydes and acids. These are exactly 
analogous to those of the methane series. A few common 
and important ones will be mentioned. 



Allyl alcohol 

Allyl aldehyde or Acrylic 

aldehyde (acrolein) 
Acrylic acid 
Crotonic aldehyde 
Crotonic acid 
Oleic acid, Ci 8 H 3 40 2 



CH 2 =CH-CH 2 OH 

CH 2 =CH-CHO 

CH 2 =CH-COOH 

CH 3 -CH=CH-CHO 

CH 3 -CH=CH-COOH 

CH 3 - (CH 2 ) 7 - CH = CH- (CH 2 ) 7 - COOH 



134 ORGANIC AGRICULTURAL CHEMISTRY 

Derivatives of allyl alcohol which contain sulphur are contained 
in oil of garlic and some containing the iso-sulphocyanate group 
are found in oil of mustard. Acrolein or acrylic aldehyde is 
the sharp smelling substance produced when glycerol or fats are 
heated. 

Oleic acid, a higher acid of the ethylene series containing 
eighteen carbon atoms and one doubly linked group of two 
carbon atoms, is found as a glycerol ester in fats and oils, 
especially in olive oil, maize oil, cotton seed oil and a small 
amount in butter. 

Linolic acid, an eighteen-carbon acid, containing, probably, 
two groups of doubly linked carbon atoms, is found as a glycerol 
ester in linseed oil. We may compare here three of the acids 
found as glycerol esters in fats, each of which contains eighteen 
carbon atoms, but two of them are poorer in hydrogen than the 
other and belong to the unsaturated series. 

C18H36O2 C18H34O2 C18H32O2 

Stearic acid Oleic acid Linolic acid 

Saturated acid Unsaturated acid Unsaturated acid 

Methane series Ethylene series 

Occurs as glyc- Occurs as glycerol Occurs as glyc- 
erol ester ester in butter erol ester in 
in beef fat. fat. linseed oil. 

These unsaturated acids, and the fats which contain their 
esters, like the hydrocarbons from which they are derived, 
readily take up bromine or iodine, forming addition compounds, 
and this reaction enables them to be distinguished and quan- 
titatively separated from the saturated acids occurring with 
them in fats and in oils. The property of drying oils which 
makes them useful in paints and injurious in lubricating oils is 
due also to the presence of these unsaturated acids, especially 
linolic acid. 

Conclusion 

In a continuation of our study beyond the point of these un- 
saturated compounds, and the compounds we have considered 



CARBOHYDRATES 135 

previously to them, we would next come to compounds in which 
carbon groups instead of being joined together in open chains, 
either straight or branched, are united to each other in the form 
of a closed chain or ring. Such compounds are known as car- 
bocyclic compounds. Chief among all the carbocyclic hydro- 
carbons is the well-known substance benzene (not benzme) 
which is obtained from coal tar. The name benzol, which is 
German, also applies to this compound. The derivatives of 
this hydrocarbon benzene (C 6 H 6 ) are even more numerous than 
those of methane, and many of them are of the greatest industrial 
importance in connection with dyeing, medicine and numerous 
industries and arts. The coal tar dyes, or aniline dyes, are 
derivatives of this class, and will suffice to give some indication 
of the importance of the compounds yet to be considered were 
we to complete our study of the compounds of carbon. 

Few of the compounds of this large series are, however, of any 
direct importance in agriculture, and as in their study we should 
gain no new general ideas of value to us in connection with agri- 
cultural chemistry we shall not do more than mention them in 
this very brief way. We shall thus bring to a conclusion at this 
point our study of the organic compounds. 

References, Section I 

Abderhalden, Neuere Ergebnisse der Eiweisschemie, 1909. 

Armstrong, The Carbohydrates and Glucosides (Monographs on Bio- 
chemistry), 191 2. 

Cohen, Organic Chemistry for Advanced Students, 1913. 

Diels, Organische Chemie, 1909. 

Holleman-Walker, Text-book of Organic Chemistry, 191 1. 

Holleman-Walker, Laboratory Manual of Organic Chemistry, 1913. 

Leathes, The Fats (Monographs on Bio-chemistry), 19 10. 

Lewkowitsch, Chemical Technology and Analysis of Oils, Fats and 
Waxes, 191 5. 

Mandel, Handbook for Bio-Chemical Laboratory, 1896. 

Meyer and Jacobson, Lehrbuch der Organischen Chemie, 1893. 

Molinari-Pope, General and Industrial Organic Chemistry, 1913. 



136 ORGANIC AGRICULTURAL CHEMISTRY 

Norris, Organic Chemistry, 191 2. 

Norris, Laboratory Manual of Organic Chemistry, 1915. 

Noyes, Organic Chemistry, 191 2. 

Osborne, The Vegetable Proteins (Monographs on Bio-chemistry), 
1909. 

Perkin and Kipping, Organic Chemistry, 191 1. 

Plimmer, Practical Organic and Bio-Chemistry, 1915. 

Plimmer, Constitution of the Proteins (Monographs on Bio-chemistry), 
1908. 

Remsen, Organic Chemistry, 1909. 

Schryver, General Characters of Proteins (Monographs on Bio- 
chemistry), 1909. 

Sherman, Organic Analysis, 191 2. 



SECTION II 



PHYSIOLOGICAL 



CHAPTER VIII 
ENZYMES AND ENZYMATIC ACTION 

Enzymes and Fermentation 

In the discussion of alcohol and its formation from glucose 
sugar by the process of fermentation we referred to the sub- 
stances known as enzymes and to the particular enzyme, zymase, 
which produces alcoholic fermentation. The action of enzymes 
or of bacteria, the latter owing their activity to the enzymes 
produced, have also been mentioned in connection with acetic 
acid, lactic acid, glucose, fructose, sucrose, starch, fats and pro- 
teins. It will thus be seen that enzymes play an important 
part in the natural formation of many organic substances. In 
fact, most of the chemical changes occurring in plants and 
animals are produced by enzymes. This important connection 
with living things makes it desirable, before we take up the 
chemistry of plant and animal physiology, to discuss briefly the 
general facts in regard to enzymes. 

The term fermentation applies to those chemical reactions 
which take place usually in connection with living organisms, 
in which the organism or substance produced by it takes no 
real part in the mass changes of the compounds involved. 
They act by their mere presence, or, as we say, catalytically, 
the chemical reaction itself being one of the ordinary type, 
such as oxidation, hydrolysis, etc. 

The word enzyme means in yeast, and signifies the fact that 
the activity of yeast is due to an enzyme or enzymes. The 
isolation of the enzyme in yeast was not accomplished, however, 
until the word had been suggested and used for some time. 
The first enzymes known were those found in the digestive 

139 



140 ORGANIC AGRICULTURAL CHEMISTRY 

fluids of animals such as ptyalin in saliva, pepsin in gastric 
juice, and diastase in the leaves and seeds of plants, etc. These 
enzymes were also termed unorganized ferments to distinguish 
them from yeast and certain bacteria which were called organ- 
ized ferments and in which the fermentation action was con- 
sidered to be due to the living organism itself. In 1897 Buch- 
ner isolated from yeast an enzyme, which he called zymase, which 
without the presence of the living yeast organism produced the 
alcoholic fermentation. This proved that in this case what 
had been considered an organized ferment was, in fact, an un- 
organized ferment or enzyme similar to the others mentioned. 

This was the beginning of the idea that all fermentation, 
whether connected with an animal or a vegetable organism or 
not, is due to the activity of substances, not of the organism itself. 
These substances or enzymes, however, are produced by the 
organism so that indirectly the organism is essential to the fer- 
mentation. Pasteur, the great French chemist and biologist, 
showed the connection between fermentation and living organ- 
isms leading to the vitalistic theory of fermentation, while 
Buchner, in isolating an enzyme from yeast, showed the relation 
of a non-living substance, produced by the organism, to the 
fermentation, thus establishing the enzyme theory of fermentation. 

Definition of Enzyme. — These facts which have been given 
lead to the definition of an enzyme as follows : 

An enzyme is a substance which acts catalytically in bringing 
about a chemical reaction of the ordinary type, the enzyme being a 
product of a living cell but acting independently of that cell. 

General Nature of Enzymes. — The exact nature of enzymes 
js unknown, though it is supposed that they are of protein char- 
acter. They are colloidal substances, non-diffusible, soluble 
in water, dilute alcohol, dilute glycerol and sodium chloride 
solution, but precipitated by strong alcohol and by a solution 
of ammonium sulphate. In general they follow the physico- 
chemical laws applying to colloids and catalysers. They act 
best at a certain optimum temperature which is, in most cases, 
approximately the temperature of the animal body, 37 C. 



ENZYMES AND ENZYMATIC ACTION 141 

Their action is inhibited at low temperatures and is destroyed 
by boiling. Each enzyme also acts best in media of a certain 
reaction as regards acidity or alkalinity. Some act in acid 
media, some in alkaline, some in neutral. The concentration 
of acidity or alkalinity is often quite definite and the action is 
inhibited or even destroyed by a different concentration or by 
a change from acid to alkaline or vice versa. It is impossible 
to say whether the enzymes that have been isolated are pure 
and individual substances or not. 

Reactions Brought About by Enzymes 

The reactions which enzymes bring about are of several kinds, 
viz. hydrolysis, oxidation, reduction, coagulation and decomposi- 
tion without extra-molecular oxidation, reduction or hydrolysis. 
The reaction of hydrolysis takes place with either carbohy- 
drates (di- and poly-saccharoses), fats or proteins. With the 
carbohydrates hydrolysis results in the resolving of the poly- 
saccharoses into their constituent monosaccharose units, e.g. 
sucrose into glucose and fructose, starch into maltose and this 
into glucose. With fats, which are glycerol esters, the hydrol- 
ysis splits the molecule into its constituent glycerol and fatty 
acid or acids. With proteins hydrolytic cleavage yields poly- 
peptides and finally amino-acids. These reactions as such have 
each been discussed under the study of the different com- 
pounds concerned. In their final products the results of 
enzymatic hydrolysis and of acid hydrolysis are the same. 

Hydrolyzing Enzymes. — The hydrolyzing or hydrolytic 
enzymes are defined further according to the compounds upon 
which they exert their catalytic effect, e.g. 

Starch-hydrolyzing enzymes are amylolytic, 

Sugar-hydrolyzing enzymes are sugar- splitting (saccharolytic) , 

Protein-hydrolyzing enzymes are proteolytic, 

Fat-hydrolyzing enzymes are lipolytic, 

Glucoside-hydrolyzing enzymes are glucoside-s putting. 
These hydrolytic enzymes are, as we shall find, mainly con- 
cerned in the digestion and metabolism of plants and animals. 



142 ORGANIC AGRICULTURAL CHEMISTRY 

Oxidizing Enzymes. — The enzymes causing oxidation re- 
actions involve in most cases the presence of atmospheric 
oxygen, though in many important cases the oxygen comes 
from other compounds rich in oxygen, such as nitrates and car- 
bohydrates. They are most important in the final oxidation 
reactions in plants and animals by which the food is oxidized 
in the cells of the organism and energy is liberated. The prin- 
cipal substance thus oxidized in the animal body is glucose, 
but it is possible that both fats and proteins are oxidized in 
this same way. 

Reducing Enzymes. — The reducing enzymes produce the 
reverse reaction to the above and are probably present in ani- 
mal and plant organisms, but no common examples can be given. 

Coagulating Enzymes. — The chemical reaction involved in 
the coagulation of proteins, e.g. the coagulation of milk casein, 
has not been established. The coagulating enzymes are found 
both in digestive fluids (milk coagulating) and in blood (blood 
clotting). 

Decomposing and Splitting Enzymes. — Those enzymes 
which cause the decomposition of the molecule without ac- 
companying extra molecular change of the preceding types 
are of two classes, (i) Sugar (monosaccharose) fermenting 
enzymes that decompose glucose or fructose and yield alcohol 
and carbon dioxide. This is the action of the yeast enzyme 
zymase. (2) Sugar-splitting enzymes that decompose a large 
molecule into a smaller one with the same percentage com- 
position, e.g. the conversion of glucose into lactic acid, 
C 6 Hi20 6 -*■ 2 C 3 H 6 3 . 

Character of Enzyme Action 

Specific Action of Enzymes. — It has been found that en- 
zymes act specifically upon certain compounds and not upon 
others. Emil Fischer believes that this specific action is due 
to the stereochemical configuration of the molecules of both 
the substance acted upon and the enzyme, i.e. that the enzyme 
and compound are related in their configuration as a key is to 



ENZYMES AND ENZYMATIC ACTION 143 

the lock. This is known as the lock-and-key theory. This 
specific action in the case of the hydrolytic enzymes is distinctly 
different from the action of acids in producing hydrolysis. 
While the hydrolysis of the different carbohydrates, fats and 
proteins may all be produced by boiling with acids or alkalies, 
an individual enzyme is necessary for each particular compound 
hydrolyzed. 

Reversible Nature of Enzyme Action. — In discussing the 
reactions of esterification and hydrolysis in connection with 
fats (p. 58) we referred to the fact that these two reactions 
represent the two directions of one of the most common rever- 
sible reactions. It is a striking fact that the fat-hydrolyzing 
enzymes especially have been found to possess the property of 
reversibility, i.e. they are able either to cause the hydrolysis 
of a fat or to esterify glycerol and a fatty acid, depending upon 
conditions, e.g. the excess of end products of the first reaction. 
The first enzyme with which this property was established was 
the one which hydrolyzes maltose sugar to glucose. Proteolytic 
enzymes have also been claimed to act reversibly. The im- 
portance of this property will be better realized when we study 
the digestion, absorption and metabolism of food. 

Zymogens 

We have referred to enzymes as occurring in plant and animal 
organisms. In some cases the enzyme does not occur as such 
and is probably not elaborated as such by the organism but in 
the form of a mother substance known as a zymogen. The 
zymogen of an enzyme is itself inactive but when acted upon 
by another substance called an activator or a kinase it is con- 
verted into the active enzyme. The best examples of this are 
the enzymes, pepsin of the gastric juice and trypsin of the pan- 
creatic juice. In the stomach cells the pepsin is not active, but 
is in the form of its zymogen known as pepsinogen. This pep- 
sinogen becomes activated by hydrochloric acid, which is a normal 
constituent of the stomach, and pepsin, the active enzyme, is the 
result. Trypsin occurs in the pancreatic juice as the zymogen, 



144 ORGANIC AGRICULTURAL CHEMISTRY 

trypsinogen. In this case the activator or kinase is another 
enzyme present in the intestinal juice known as enter okinase. 
When these two substances, the trypsinogen and enterokinase, 
come together, the active enzyme trypsin is the result. The 
activator may thus be another enzyme or a non-enzyme sub- 
stance like hydrochloric acid. 

Co-enzymes and Anti-enzymes. — It has also been shown 
that an enzyme may not be a single unit, but may consist of two 
parts known as the enzyme and the co-enzyme. The activity of 
the enzyme is dependent upon the presence of its complement 
the co-enzyme. These two substances have been separated 
in the case of the enzyme zymase and activity results only when 
the two are present together. The nature of the co-enzyme is 
not well established. 

Also there have been shown to be substances present in the 
animal body which prevent the action of certain enzymes. 
These have been called anti-enzymes. These anti-enzymes are 
exceedingly important and are connected with the action of 
toxins and the condition known as immunity. 

Without going into detail we have thus presented the main 
known facts and theories in regard to enzymes and enzymatic 
action. What has been said will help us to understand what 
will be presented later on in connection with the digestion, 
absorption and metabolism of food both in plants and in ani- 
mals. In all of the chemical reactions connected with the phys- 
iological processes of living organisms enzymes are, no doubt, 
the catalytic agent. In both plants and animals they are 
abundant, probably much more so than our present knowledge 
establishes. It may emphasize their importance in animal 
physiology to state that in the liver alone there are probably 
fifteen or more distinct enzymes that have been shown to be 
active. 

Names of Enzymes 

The name of an enzyme, where a systematic name has been 
applied, is made up from the name of the substance upon which 
the enzyme acts and the termination ase. The enzymes re- 



ENZYMES AND ENZYMATIC ACTION 



145 



f erred to already which act upon starch, hydrolyzing it to maltose 
sugar, are known as amyl-ases, the prefix amyl coming from the 
word amylum for starch. Similarly, an enzyme hydrolyzing 
sucrose is known as sucrase, one hydrolyzing maltose as maltase. 
In the same way fat-splitting or lipolytic enzymes are lipases 
and protein-hydrolyzing enzymes are proteases. 

A brief list of the more important plant and animal enzymes 
may be given. 

TABLE IV 
Enzymes 



Enzyme 


Action 


Group Name 


Where 

Found 


Substance 
Acted 
Upon 


Products 


Ptyalin 


Hydrolysis 


Animal 
Amylase 


Saliva 


Starch 


Maltose 


Diastase 


Hydrolysis 


Plant 
Amylase 


Leaves 
Seeds 


Starch 


Maltose 


Amylopsin 


Hydrolysis 


Pancreatic 
Amylase 


Pancreatic 
juice 


Starch 


Maltose 


Sucrase or 


Hydrolysis 


Saccharase 


Intestinal 


Sucrose 


Glucose, 


Invertase 




(Sugar-split- 
ting) 


juice 




Fructose 


Maltase 


Hydrolysis 


Saccharase 
(Sugar-split- 
ting) 


Intestinal 
juice 


Maltose 


Glucose 


Lactase 


Hydrolysis 


Saccharase 


Intestinal 


Lactose 


Glucose 






(Sugar-split- 


juice 




Galactose 






ting) 








Pepsin 


Hydrolysis 


Protease 


Gastric juice 


Protein 


Proteoses, Pep- 
tones, Pep- 
tides 


Trypsin 


Hydrolysis 


Protease 


Pancreatic 
juice 


Protein 


Proteoses, Pep- 
tones, Pep- 
tides, Amino- 
acids 


Erepsin 


Hydrolysis 


Protease 


Intestinal 
juice 


Proteoses 
Peptones 


Amino-acids 


Steapsin 


Hydrolysis 


Lipase 


Pancreatic 
juice 


Fats 


Glycerol 

Fatty acids 


Rennin 


Coagulation 


Coagulating 


Gastric juice 
Pancreatic 
juice 


Caseino- 
gen 


Casein 


Enterokinase 


Activates 


Kinase 


Intestinal 
juice 


Trypsino- 
gen 


Trypsin 


Emulsin 


Hydrolysis 


Glucoside- 


Bitter 


Amygda- 


Glucose, Benz- 






splitting 


almonds 


lin 


aldehyde, 
HCN 


Oxidases 


Oxidation 










Reductases 


Reduction 










Zymase 


Decompo- 
sition 


Glucose-fer- 
menting 


Yeast 


Glucose 


Alcohol, C0 2 



CHAPTER IX 

THE COMPOSITION OF PLANTS AND 
ANIMALS 

In our study of the organic compounds which are of im- 
portance in connection with plants and animals from the agri- 
cultural standpoint we gave especial attention to three groups, 
viz. carbohydrates, fats and proteins. These three groups com- 
prise all of the essential organic food materials of both plants and 
animals. Only relatively few compounds outside of these three 
groups were mentioned, for example, lactic, malic and tartaric 
acids, some of the esters in addition to the glycerol esters or 
fats, urea, uric acid and some others. The last two we shall 
find are physiologically directly connected with the proteins. 
The others, and some which were not mentioned at all, while 
they are no doubt essential to the life history and environment 
of the plant or animal, are nevertheless not essential in the same 
way as the carbohydrates, fats and proteins, i.e. as food ma- 
terials. As the relationship of plants and animals to their food 
supply is the primary one in their agricultural connection we 
see that in a study of agricultural chemistry these three groups 
of compounds occupy a predominant position. 

Organic and Inorganic Constituents. — In their chemical 
composition plants and animals may be readily shown to con- 
sist of two distinctly different kinds of material, viz. organic 
and inorganic. Considering the definition of organic com- 
pounds which we derived from our study of organic chemistry, 
we term organic any compound which in its constitution is 
proven to be derived from the fundamental compounds of carbon 
and hydrogen, the hydrocarbons. As such, the organic com- 
pounds present in plants and animals contain, in most cases, 

146 



THE COMPOSITION OF PLANTS AND ANIMALS 147 

the elements carbon, hydrogen and oxygen with nitrogen and 
sometimes also sulphur and phosphorus in the important group 
of the proteins. Some few other elements may also occur in 
strictly organic combination, but these six elements are the con- 
stituents of practically all of the organic compounds of both 
plants and animals. 

The inorganic compounds present in plants and animals con- 
sist mainly of the metallic elements, potassium (K), sodium 
(Na), calcium (Ca), magnesium (Mg) and iron (Fe), in com- 
bination, mostly as salts, with the nonmetallic elements chlorine 
(CI), sulphur (S), phosphorus (P), nitrogen (N) and oxygen (O). 
Aluminium (Al), arsenic (As) and some others may also be 
present. It is not always possible to determine whether these 
elements that we consider inorganic are present in the living 
plant or animal in true inorganic combination as salts or whether 
they really are part of a true organic compound containing also 
carbon, hydrogen, oxygen, nitrogen, etc. We know, for ex- 
ample, that in the blood, urine and gastric juice of animals we 
find such compounds as sodium chloride, calcium phosphate 
and hydrochloric acid, which are evidently present as such in 
these liquids. On the other hand we believe that in the blood 
the iron which is present is unquestionably in the form of a true 
organic compound, a protein known as hemoglobin. Also in 
chlorophyll, a constituent of green leaves, magnesium is present 
as part of a true organic compound, and in milk the metallic 
element calcium is present as part of one of the protein constit- 
uents. Thus, if we should consider as organic any substance 
present as part of the living material of a plant or animal, it is 
probable that most of the inorganic elements mentioned should 
be classed as in organic combination. 

Volatile and Nonvolatile Constituents. — The separation of 
the constituents of plants and animals into organic and in- 
organic may be easily accomplished in an approximate way by 
simply burning the plant or animal substance in the air. When 
thus burned in the air the organic constituents consisting in 
general of the six elements previously mentioned are converted 



148 ORGANIC AGRICULTURAL CHEMISTRY 

by oxidation into gaseous or volatile products which disappear, 
while the inorganic constituents are converted into nonvolatile 
compounds which remain. Thus, generally speaking, the 
organic constituents yield volatile products on burning, and the 
inorganic constituents yield nonvolatile. 

If we were dealing with pure organic constituents by them- 
selves, such as pure carbohydrates, fats or proteins, we should 
find this to be wholly true. On burning in air the carbon would 
be converted into carbon dioxide gas, CO2, the hydrogen into 
water, H 2 0, the nitrogen into free nitrogen, N, the sulphur would 
yield the gas sulphur dioxide, SO2, and the phosphorus would be 
oxidized to phosphorus pentoxide, P2O5, a solid. All of these 
products, whether gases, liquids or solids, would be volatilized 
at the temperature of the combustion and would thus disap- 
pear. In a like manner the pure inorganic constituents by 
themselves would be left on burning in the form of oxides, 
carbonates, chlorides, sulphates, nitrates or phosphates, depending 
largely upon the original form in which they were present. 

However, on burning any mixed plant or animal material 
the two sets of products are present together and a sharp sepa- 
ration does not take place. All of the hydrogen of the organic 
constituents disappears in the form of water vapor. A large 
part of the carbon likewise goes off as carbon dioxide gas. 
Some of the carbon dioxide, however, which is formed from the 
carbon of organic compounds, in the presence of the metallic 
elements of the inorganic constituents, unites with the oxides 
of these metals and remains as nonvolatile carbonates, e.g. 
potassium carbonate, K2CO3. The sulphur and nitrogen also, 
instead of being completely volatilized, combine with the metal 
oxides as sulphates and nitrates, e.g. sodium sulphate, Na 2 S04, 
potassium nitrate, KN0 3 . Likewise, the phosphorus from 
organic compounds will not volatilize, but will remain non- 
volatile as a phosphate of some metal, e.g. calcium phosphate, 
Ca 3 (P0 4 ) 2 . Also any iron, calcium or other metallic element, 
although present as part of a true organic compound, will re- 
main after combustion in the form of some nonvolatile salt. 



THE COMPOSITION OF PLANTS AND ANIMALS 149 

Ash. — On burning a plant or animal substance the non- 
volatile products as described above will be left in the form of a 
gray or white ash. This ash represents the nonvolatile products 
of the combustion and contains all of the inorganic constituents 
and some part at least of the carbon, nitrogen, sulphur and phos- 
phorus of the organic constituents together with any metallic 
elements which may have been present in organic combination. 
Therefore, this simple separation of a plant or animal substance 
into volatile and nonvolatile products does not correspond 
exactly to the organic and inorganic constituents present. It 
does, however, indicate approximately their relative amounts. 

On making such a separation of the volatile and nonvolatile 
products of combustion and determining the amounts present, 
it is found that the organic constituents yielding volatile products 
are much in excess of the inorganic constituents which yield 
the nonvolatile products, or ash. The number of different 
elements present in the latter are more than those in the former. 

The table on pages 1 50-1 51 gives some results of the deter- 
mination of volatile and nonvolatile or ash constituents in some 
common plant materials. 

We have thus shown that plants and animals consist of both 
organic and inorganic constituents. The two classes of ma- 
terials are, therefore, both essential to the life of the organism. 
In animals, the skeleton portion of vertebrate animals is largely 
inorganic, being chiefly calcium phosphate, Ca 3 (P0 4 ) 2 . The 
other inorganic constituents are found mostly in the liquids or 
secretions of the animal body such as blood, milk, urine and the 
digestive fluids. All of these inorganic substances play an 
important role in the life of the animal. Their action is, how- 
ever, not well understood in most cases and is at least distinctly 
different from the action of the organic constituents. We shall, 
therefore, not consider them in detail, simply stating that in the 
animal body they are formed from the inorganic materials in 
the food which the animal eats. 

In plants the inorganic constituents are related directly to 
the soil, from which source the plant obtains its food material 



150 ORGANIC AGRICULTURAL CHEMISTRY 

TABLE V 

Volatile and Nonvolatile Constituents 









Volatile 




Plant or Plant 
Product 


Water 


Ash 


Constituents 

Other Than 

Water 




Maize (Flint) .... 


11.3 


1.4 


87.3 


J. & W., pp. 12-19 


Maize (sweet) (Mass.) . 


8.7 


1.8 


89-5 


J. & W., pp. 12-19 
(Bui. 120, p. 33) 


Wheat (spring) .... 


10.4 (9.94) 


1.9 (1.94) 


87.7 (88.12) 


J. & W., pp. 12-19 
(Bui. 120, p. 33) 


Wheat (winter) . . . 


10.5 (10.55) 


1.8 (2.0) 


87-7 (87.4S) 


J. & W., pp. 12-19 
(Bui. 120, p. 33) 


Sorghum grain .... 


12.8 (11.71) 


2.1 (1.75) 


85.1 (86.54) 


J. & W., pp. 12-19 
(Bui. 120, p. 42) 


Barley 


10.9 (9.32) 


2.4 (3.04) 


86.7 (87.64) 


J. & W., pp. 12-19 
(Bui. 120, p. 36) 


Rye 


11.6 (9-38) 


1.9 (2.18) 


86.5 (88.44) 


J. & W., pp. 12-19 
(Bui. 120, p. 35) 


Oats 


11.0 (7.82) 


3-o (3-96) 


86.0 (88.22) 


J. & W., pp. 12-19 
(Bui. 120, p. 24) 


Rice 


12.4 


0.4 


87.2 


J. & W., pp. 12-19 


Wheat middlings . . . 


12. 1 


3-3 


84.6 


J. & W., pp. 12-19 


Wheat bran 


11.9 


5-8 


82.3 


J. & W., pp. 12-19 


Maize stalks (green) . . 


76.1 


0.7 


23.2 


J. & W., pp. 12-19 


Maize stalks (cured) . . 


68.4 


1.2 


30.4 


J. & W., pp. 12-19 


Maize stover (cured) . . 


40.1 


3-4 


56.5 


J. & W., pp. 12-19 


Maize fodder (green) . . 


79-8 


1.1 


19.1 


J. & W., pp. 12-19 


Maize fodder (cured) . . 


42.2 


2.7 


55-1 


J. & W., pp. 12-19 


Maize silage .... 


79-1 


1.4 


19-5 


J. & W., pp. 12-19 


Wheat straw .... 


9-6 


4.2 


86.2 


J. & W., pp. 12-19 


Oat straw 


9.2 


5-i 


85-7 


J. & W., pp. 12-19 


Timothy grass .... 


61.6 


2.1 


36.3 


J. & W., pp. 12-19 


Timothy hay .... 


13-2 


4.4 


82.4 


J. & W., pp. 12-19 


Red clover, grass . . . 


70.8 


2.1 


27.1 


J. & W., pp. 12-19 


Red clover hay .... 


15-3 


6.2 


78.5 


J. & W., pp. 12-19 


Alfalfa, grass .... 


71.8 


2.7 


25-5 


J. & W., pp. 12-19 


Alfalfa hay 


8.4 


7-4 


84.2 


J. & W., pp. 12-19 


Cowpea (fresh) .... 


83.6 


1-7 


14.7 


J. & W., pp. 12-19 


Cowpea (cured) . . . 


10.7 


7-5 


81.8 


J. & W., pp. 12-19 


Cowpea (peas only) . . 


14.8 


3-2 


82.0 


J. & W., pp. 12-19 


Soja beans (fresh) . . . 


74-8 


2.4 


22.8 


J. & W., pp. 12-19 


Soja beans (bean only) . 


10.8 


4-7 


84.5 


J. & W., pp. 12-19 


Potatoes 


78.9 


1.0 


20.1 


J. & W., pp. 12-19 


Sweet potatoes .... 


71. 1 


1.0 


27.9 


J. & W., pp. 12-19 


Red beets 


88.5 


1.0 


10.5 


J. & W., pp. 12-19 


Sugar beets 


86.5 


0.9 


12.6 


J. & W., pp. 12-19 



THE COMPOSITION OF PLANTS AND ANIMALS 151 



Plant os Plant 
Prodvct 



Turnips 

Carrots 

Mangels 

Rutabaga 

Onion 

Cabbage 

Asparagus 

Spinach 

Barley, malt sprouts . . 

Gluten meal 

Germ meal 

Cottonseed meal . . . 
Linseed meal (new pro- 
cess) 

Flaxseed (ground) . . 

Cottonseed 

Castor oil bean .... 

Sesame seed 

Rape seed 

Cacao bean (unshelled) . 

Coconut 

Palm nut (kernel) . . . 

Brazil nut 

English walnut (dry) . . 

Peanut 

Olive (pulp) 

Olive seed (without shell) 

Apple 

Peach 

Strawberry 

Pineapple 

Banana 

Orange 

Lemon 

Grape 

Sugar cane 

Cotton fiber (American) 

Cassava root . . . . 



Water 



9°-5 
88.6 
90.9 
88.6 
87.6 

90. S 

94.0 
92.4 
10.2 

9-6 
10.7 

8.2 

10.1 

8.9 

9-3 

6.5 

5-5 

7-3 

6.4 

5.8 

8.4 

5-9 

7.2 

7-5 

24.2 

6.2 

84.4 

83.0 

87.0 

89-3 

74-9 

84-3 

82.6 

79.1 

75-4 

8.0 

70.2 





Volatile 








Constituents 




Ash 


Other Than 






Water 




0.8 


8.7 


J. & W., pp. 12-19 


1.0 


10.4 


J 


& W., pp. 12-19 


1.1 


8.0 


J 


& W., pp. 12-19 


1.2 


10.2 


J 


& W., pp. 12-19 


0.6 


11.8 


J 


& W., pp. 12-19 


1.4 


8.1 


J 


& W., pp. 12-19 


0.7 


5-3 


J 


& W., pp. 12-19 


1.9 


5-7 


J 


& W., pp. 12-19 


5-7 


84.1 


J 


& W., pp. 12-19 


0.7 


89.7 


J 


& W., pp. 12-19 


4.0 


85.3 


J 


& W., pp. 12-19 


7.2 


84.6 


J 


& W., pp. 12-19 


5-8 


84.1 




4-3 


86.8 


Kdnig, p. 606 


4-5 


86.2 


Konig, p. 615 


3-1 


90.4 


Konig, p. 613 


6-5 


88.0 


Konig, p. 613 


4.2 


88.5 


Konig, p. 607 


4.0 


89.6 


Konig, p. 1022 


1.8 


92.4 


Konig, p. 616 


1.8 


89.8 


Konig, p. 614 


3-9 


90.2 


Konig, p. 616 


1.6 


91.2 


Konig, p. 615 


2-5 


90.0 


Konig, p. 615 


2.7 


73-1 


Molinari, p. 391 


2.2 


91.6 


Molinari, p. 391 


0.4 


15-2 


Konig, p. 823 


0.6 


16.4 


Konig, p. 829 


0.7 


12.3 


Konig, p. 840 


0.4 


10.3 


J. & W., p. 92 


1.0 


24.1 


Konig, p. 852 


0.4 


15-3 


Konig, p. 849 


0.6 


16.8 


Konig, p. 849 


o-S 


20.4 


Konig, p. 842 


0.7 


23-9 


Konig, p. 896 


O.I 


91.9 


Bowman (Haas & 
Hill), p. 129 


0.5 


29-3 


Konig, p. 149s 



" J. & W. ": Jenkins & Winton, American Feeding Stuffs, U. S. Dept. Agr. O. E. S. Bui. 11, 
1892. "Konig": Chemie der Mensch. Nahr. u. Genussmittel, vierte Auf. 1903. "Bui. 
120" : Chamberlain, Feeding Value of Cereals, U. S. Dept. Agr. Bur. Chem. Bui. 120, 1909. 
" Molinari " : Molinari, General and Industrial Organic Chemistry, Eng. Ed. 1913. " Haas & 
Hill " : Haas & Hill, Chemistry of Plant Products, 19 14. 



152 ORGANIC AGRICULTURAL CHEMISTRY 

of this character. In the soil this inorganic food is present in 
the form of salts, principally as nitrates, phosphates, chlorides 
and sulphates of potassium, sodium, calcium and magnesium. 
These salts constitute what is termed the soil plant food. 
They are also the constituents of substances used to supply an 
abundance of soil plant food in the form of manure or commer- 
cial fertilizers, the latter being mostly of three kinds, viz. 
nitrate, phosphate and potassium salts. All of this relationship 
of the plant to the soil and to fertilizers is part of the study of 
Inorganic Agricultural Chemistry. We shall, therefore, not 
say anything further in regard to the inorganic constituents of 
plants and give only slight references to the inorganic constit- 
uents of animals. The chapters which follow will deal pri- 
marily with the organic constituents and will endeavor to show, 
by general and well-established facts, how these constituents 
are produced, what their function is and how this function is 
carried out. 

EXPERIMENT STUDY XXVI 

Organic and Inorganic Constituents of Plants and Animals 

(i) Organic or Volatile Constituents, (a) Place i.o g. of pure dry 
wheat starch or potato starch in a porcelain crucible or evaporating 
dish. Heat the dish gradually with low flame. Note charring of 
the starch, indicating free carbon. As fumes are given off hold a test 
tube, dry on outside but half full of cold water, in the vapor. Note 
deposit of water vapor. Increase the heating, and hold in the vapor 
a glass tube that has been dipped in limewater. A cloudy appear- 
ance of the limewater on the tube shows presence of carbon dioxide 
in the vapor. Continue to heat with full flame until all free carbon 
has disappeared. What is the source of carbon ? What has become 
of it? What other elements are shown to have been present in the 
starch? Is there any ash left? (b) Repeat the experiment, using 
pure fat, e.g. lard or cottonseed oil. (c) Repeat again, using pure 
protein, e.g. white of egg or wheat gluten. 

(2) Inorganic or Nonvolatile Constituents, (a) Weigh a small 
porcelain evaporating dish that has been previously cleaned, dried 



THE COMPOSITION OF PLANTS AND ANIMALS 153 

by heat and cooled in a desiccator. Weigh into this dish 10.0 g. of 
dry grass, straw or leaves. Heat the dish slowly, testing the volatile 
products as in (1). Heat with full flame until all free carbon has been 
oxidized. When only a light gray ash is left, cool the dish in a desic- 
cator and weigh. Subtract the weight of the dish from the weight 
of dish and ash to obtain the weight of ash. Calculate the per cent 
in the original material. The difference between this and 100 per 
cent will give the per cent of volatile or organic constituents in the 
original substance. In the ash obtained from most mixed plant and 
animal materials we may show the presence of the following metallic 
elements and salts: (1) sodium, Na, potassium, K, calcium, Ca, 
magnesium, Mg, carbonates, Na 2 C0 3 , nitrates, KNO3, phosphates, 
Na 3 P0 4 , sulphates, K 2 S0 4 , chlorides, NaCl. 

(b) Evaporate 25 c.c. of milk, blood, urine or saliva slowly to dry- 
ness and repeat (a) with dry residue. 



CHAPTER X 
THE LIVING CELL AND ITS FOOD 

Plant and Animal Cell Alike. — At the very beginning of our 
study of the chemical processes of plants and animals we must 
emphasize the important fundamental fact that, as living 
organisms the plant and the animal are alike. Each individual 
plant and each individual animal is composed of an aggrega- 
tion of simple cells, and the fundamental chemical processes of 
these living cells are alike. The life of the complex individual 
is but the total of the lives of all the cells of which it is composed. 
Thus, to understand the chemical processes of the individual 
we must first understand the chemical processes of the living cell. 

We do not wish to give the impression that the whole ques- 
tion of life is simply one of chemical reaction. We may under- 
stand the chemical reactions which take place together with the 
physical conditions under which they occur without being able 
to explain the phenomenon of life itself. As a great German 
biochemist has said, 1 " Physiology cannot really be identical with 
the chemistry and physics of living organisms." Furthermore 
it is only a small part of the reactions involved in living organ- 
isms which we as yet do understand or which are so clearly demon- 
strated that they are proper subjects for discussion in this study. 

Composition of the Cell. — Biologically considered the living 
cell is characterized by containing the substance known as pro- 
toplasm. This substance is essential to living matter. Chemi- 
cally its composition is not definitely known, but it has been 
defined as a solution of protein containing also carbohydrates, 
fats and inorganic salts, either in solution or colloidal suspen- 
sion. Thus all living matter contains these three groups of 
organic compounds, carbohydrates, fats and proteins. 

1 Czapek, "Chemical Phenomena in Life," 191 1. 
154 



THE LIVING CELL AND ITS FOOD 



155 



Cell Energy and Cell Food. — The living cell, whether plant 
or animal, performs its function of life through the agency of 
energy which is set free by its utilization 0} food supplied to it 
from without. When we study later the peculiar processes or 
functions of plants which differentiate them from the animals 
we shall find that the ultimate source of this energy is the sun. 
For the present, however, and so far as the cell itself is con- 
cerned, the source of the cell's energy is its food. We have just 
stated that the cell is composed of carbohydrates, fats and pro- 
teins and inorganic salts. It is clear, therefore, that the food 
of the cell must contain these same substances. So far as we 
know the inorganic constituents of the cell or of the cell food 
have nothing to do, at least directly, with the energy of the cell. 
In its energy relationship, therefore, the food of the cell is 
wholly organic of the three groups of compounds mentioned. 
This is borne out by the fact that the seeds of plants which 
contain the germ of a new plant have stored within them all 
of these constituents, and these are used by the developing 
embryo as food. Also all animals require as food, not one 
only, but all of these groups of compounds. 

Food as Energy Material. — How then do these organic 
substances which we may term energy food yield this energy to 
the living cell and thus to the whole living organism ? If we 
recall the chemical composition and constitution of these com- 
pounds we see that they are alike in being complex compounds 
of carbon, hydrogen and oxygen, with nitrogen in addition to 
these in the proteins. The percentage composition of the three 
groups of compounds is : 



Carbohydrates 


Fats 


Proteins 


C 6 Hi 2 6 (Glucose) 

C. 40.00 per cent 
H. 6.66 per cent 
O. 53-33 Per cent 

N. 

S. — - 


CsiHggOe (Glyceryl tri- 

palmitate) 
75.93 per cent 
12.16 per cent 
1 1. 91 per cent 


51.00-55.00 per cent 

6.00- 7.00 per cent 

20.00-25.00 per cent 

15.00-17.6 per cent 

0.3 - 2.5 per cent 



156 ORGANIC AGRICULTURAL CHEMISTRY 

They all contain large amounts of carbon and hydrogen in 
proportion to the oxygen. This is not so clear from the per- 
centage composition as when we consider the atomic relations 
of the elements present. The two elements, carbon and 
hydrogen, unite readily with oxygen, forming carbon dioxide, 
CO2, water, H 2 0. In the carbohydrates only, in which 
oxygen is in the greatest amount and hydrogen the least, is 
there enough oxygen to combine with the hydrogen when the 
compound is decomposed. When therefore these compounds 
are brought in contact with free oxygen under certain condi- 
tions, e.g. at raised temperatures or through the agency of 
enzymes, then the carbon and the excess hydrogen will become 
oxidized or, as we say, the substance burns. This reaction is 
the basis for the characterization of these organic constituents 
of plants and animals as volatile or combustible. Now when 
this reaction of oxidation takes place and the complex com- 
pounds are thus decomposed into simpler oxygen compounds, 
energy is set free. We indicate this in the reaction by writing 
it as follows, using the carbohydrate glucose as our example : 

C 6 Hi20 6 + 6 2 -> 6 C0 2 + 6 H 2 + energy 
Glucose 

Each of the other compounds, viz. fats and proteins, under- 
goes a similar oxidation with the liberation of energy. We shall 
find later that each of the three compounds yields, per gram 
or ounce of substance, a different but definite amount of energy. 

Oxidation of Food. — Now when the living cell utilizes its 
food, this reaction of oxidation takes place and energy is set 
free, and it is this energy that is the energy of the living cell. The 
reaction is not always as simple as we have written it and it 
may take place only partially or in several steps, but the result 
is the liberation of a whole or a part of the energy of such a 
complete reaction. 

Heat and Work. — In the reaction as it takes place in the 
air or in oxygen, the energy liberated manifests itself in the form 
of heat, i.e. the substance burns. Such a manifestation of the 



THE LIVING CELL AND ITS FOOD 157 

energy is not, however, always the result. When the oxidation 
occurs in the cell it is probably always due to the influence of 
enzymes, and the energy set free may be in the form of heat 
which is not accompanied with burning, as we ordinarily think 
of it, but in the form of heat that maintains a certain temper- 
ature such as the body heat of warm-blooded animals. The 
energy may not, however, produce heat at all, but may be 
manifested in the form of muscular work, as in the case of ani- 
mals or of work not exactly muscular but which may be called 
cellular, such as is required in the growth of large plants or trees. 

The fundamental chemical reaction of living cells, then, is the 
oxidation of the complex organic compounds of the food to simple 
compounds with the liberation of energy, which energy is the 
basis of the living process manifesting itself as heat or work in 
the various functions and properties of the living organism 
whether the organism is plant or animal. 

Food as Building Material. — Not only must the living cell 
be furnished with food which by oxidation yields energy, but it 
must also utilize its food for building up its own substance. This 
will necessarily be much greater in the cases of young and rapidly 
growing organisms, but in all organisms cell substance is con- 
tinually used up in the life process and new building material 
must be supplied. We cannot state as a positive fact that all 
food is first converted into cell substance or, as we say, body 
substance, before it is oxidized, but it is at least probable that 
this is so. We know that if an animal is deprived of food it 
utilizes its own body substance, which is torn down and oxidized, 
thus yielding the energy necessary for life. 

Function of Food. — Thus the function of food may be con- 
sidered as twofold, i.e. to build body or cell substance and to 
furnish energy. 

Plants and Animals Compared 

Each plant or animal of the higher forms, and it is only these 
higher forms that we shall consider, is a very complex individual. 
The single cells of which the organism is composed do not per- 



158 ORGANIC AGRICULTURAL CHEMISTRY 

form their functions separately, but are united into different 
tissues and organs, and the functions of the various tissues and 
organs are very different. Thus, while as stated above the indi- 
vidual cells are alike in their fundamental chemical processes, 
the net result of the processes of all the cells, or, as we may 
say, the predominating reaction, is distinctly different so that the 
single plant bears little resemblance to the single animal. 

In the animal organism, particularly in the mature animal, 
as we shall find, the two functions of food are practically re- 
solved into one, for food material which is converted into body 
substance is eventually oxidized for the production of energy. 
Only a small part of the food is utilized to build body substance 
which is not later oxidized, and this material is largely the in- 
organic portion. The net result of the physiological processes of 
animals or, as we may say, the predominating physiological 
process of animals, is the utilization of food for the production of 
energy and this energy is manifested as animal work or animal 
heat In the plant organism, however, the two functions re- 
main more distinct. Only a small part of the food is utilized 
for the production of energy. The greater part is built up by 
means of this energy into body substance which becomes either 
reserve food or structural material. The net result of the phys- 
iological processes of plants is thus the formation of body sub- 
stance. These distinctly different net results are correlated 
with distinctly different physiological processes in plants and 
animals which differentiate them from each other and which 
we shall consider later as we study each kind of organism. 

With these distinct differences between plants and animals 
which we shall discuss we must not lose sight of the fact, first 
stated at the beginning of this chapter, that in their fundamental 
reaction plant cells and animal cells are alike, and this funda- 
mental reaction is the oxidation of the three organic food con- 
stituents, whereby energy is liberated and this energy is the 
energy of the life process. 



CHAPTER XI 

ANIMAL FOOD AND NUTRITION 
DIGESTION AND ABSORPTION 

ANIMAL FOOD 

We have now to consider the question as to how and in 
what form the food reaches the cell and how the fundamental 
oxidation reaction is brought about. It is impossible to in- 
vestigate these processes with the single cell, but as the animal 
organism as a whole utilizes its food for the production of energy 
just as the single cell does, we are able to understand the chemical 
reactions by which food is eventually converted into energy by 
making a study of the way in which it is accomplished in the 
animal body. Furthermore, it is not possible to study these 
processes in the plant with the same detail that we can in the 
animal for the simple reason that they have not yet been worked 
out in the plant, because in the plant they are masked or over- 
shadowed by the predominating constructive processes. We 
shall, therefore, turn our attention from the single cell as such, 
which is alike in its fundamental chemical processes in both 
plants and animals, to the consideration and study of the animal 
as a whole and the chemical processes by which it utilizes its 
food material primarily for the liberation of energy. 

Definition of Food. — As we have previously stated in a 
general way, the chemical composition of the animal body 
while it is made up of very complex individual compounds is, 
nevertheless, simple in that they are all comprised in the three 
groups, carbohydrates, fats and proteins, together with some 
inorganic salts. These latter are found mostly in the skeleton 
part of vertebrate animals and in small amounts in the various 
animal fluids, where they perform important functions, but in 

iS9 



160 ORGANIC AGRICULTURAL CHEMISTRY 

which functions they bear no direct relation to the energy of 
the living animal. Different animals and different organs of 
the same animal contain different individual compounds of the 
three groups, but, considered as a whole, and in general, the 
living cellular portions of the animal body are composed of 
carbohydrates, fats and proteins. It will thus be natural to 
find that the organic or energy food of animals consists of these 
three groups of compounds, for out of these food materials the 
body substance of the animal must be formed and from them 
the energy of the animal is derived. 

Animal food has been defined as " anything, which taken into 
the animal body is utilized by the animal for the building up of 
body substance or for the production of energy." 

Utilization of Food. — In order that the miscellaneous food 
may thus be utilized to build cellular material or to furnish 
energy by oxidation, it is necessary for it to undergo certain 
changes. In other words, the food material must fit the condi- 
tions of the animal body. The changes which the food thus 
undergoes are included in the various processes known by the 
general name of digestion. 

After the food has been put in the proper condition by the 
processes of digestion, it must then be taken up by the circulating 
fluid of the body and conveyed to the cells and organs where 
later changes occur. This process is known as absorption. 
The digested and absorbed food then undergoes other changes 
necessary for conversion into body substance or for oxidation. 
These changes are included in the processes known as metabolism. 
The final change in metabolism is always oxidation with the 
liberation of energy and the formation of certain waste prod- 
ucts. These waste products are then eliminated from the body 
by the processes of excretion. 

Thus the food is subjected to the two main processes of 
digestion and metabolism, with the secondary processes of 
absorption and excretion. For the purpose of considering the 
food of animals we may, therefore, divide the animal body into 
four regions, viz. {a) the region of digestion, where the food is 



DIGESTION AND ABSORPTION 161 

converted into conditions necessary for absorption and metabo- 
lism, (b) the region of absorption, where the digested food is 
taken up and conveyed to the cells, (c) the region of metabolism, 
where the digested and absorbed food is built up into body 
substance, or is oxidized, (d) the region of excretion, where the 
products of metabolism are removed from the body. It must 
be noted that these are not regions defined anatomically by 
location in certain organs but by the process which takes place. 

We shall now consider each one of these processes in the order 
in which they take place in the animal body. In the following 
discussion of the physiological processes of animals the facts 
refer primarily to human beings. In general they apply also 
to domestic animals, but in cases where they are known to be 
different some qualifying statement will be made. 

Mastication or Chewing. — The mastication of the food in 
the mouth, or in other regions where this is accomplished in 
some animals, as the gizzard of fowls, is not, strictly speaking, 
part of the process of digestion. In most cases it must precede 
digestion and is part of the physical operation by which the 
food is obtained and introduced into the animal body in a proper 
condition for digestion. It results in the finer division of the 
food substance so that it will be in such a physical condition 
that digestive juices may act upon it. It will naturally vary as 
the character of the food substances varies. In the case oi\ 
liquid foods or foods already in solution no mastication is neces- 
sary. We must caution against assuming from what has 
previously been said that all soluble substances are on that 
account already digested and do not need digestive action. A 
soluble substance, as we shall soon explain, may or may not be 
subject to digestion. For each food constituent there is a final 
form which it must assume before it can be absorbed and 
metabolized. The food material in a few cases may be already 
in this form, but it may also be readily soluble and still require 
digestion. The solid foods require more or less thorough 
mastication in order to make them subject, under the best 
conditions, to digestive action. Plainly, the tougher and 



162 ORGANIC AGRICULTURAL CHEMISTRY 

harder the solid food the more thorough must be the mastica- 
tion. This is why the food of herbivorous animals like the 
horse and cow must be subject to the most thorough mastica- 
tion, and in the latter animal and other ruminants is subject 
to a second mastication. Mastication in all the common 
animals, except the fowls, takes place in the mouth by means 
of the teeth. Thus we find that animals which naturally eat 
the tougher foods, like raw plants, have the more elaborate 
and stronger masticating teeth. 

Digestion. — The animal body is composed of material 
more or less saturated with water. All of the body fluids are 
water solutions or suspensions and the cells contain water 
solutions. The cell walls are membranes permeable to water 
and semipermeable to substances in solution. A living cell 
which is thoroughly dried becomes dead as a consequence. 
The whole body may thus be considered as a water system. 
Thus solubility in water and permeability through cellular 
membranes are necessary conditions for food material that is to 
be absorbed and built up into body substance. Of the three 
organic food constituents the carbohydrates are the only ones 
that are soluble in water to any extent. Even of the carbo- 
hydrates the most widely distributed member considered as a 
food is starch which is insoluble. The fats are wholly in- 
soluble and of the proteins only one group, viz. the albumins, 
is soluble in water. The conversion of the insoluble forms of 
food material into soluble is thus essential and is brought about 
by the process of digestion. 

Not only, however, must the food material be soluble, but 
it must be brought into certain definite forms so that the sub- 
sequent changes of metabolism may take place. This may be 
illustrated by the fact that though cane sugar and milk sugar 
are soluble compounds they, nevertheless, undergo digestive 
changes, because in their unchanged character they cannot be 
built up into body substance or oxidized. 

We may, therefore, say that the object of digestion is two- 
fold: first, to convert insoluble food materials into soluble com- 



DIGESTION AND ABSORPTION 163 

pounds in order to meet the conditions of a system saturated 
with water ; second, to convert the miscellaneous food material 
into certain uniform compounds to meet the conditions of 
further metabolic change. 

(So far as we know the inorganic compounds which serve as 
food do not require digestive action, so that the process of 
digestion has to do entirely with the organic constituents*^ 
In the following discussion we shall take up each one of the 
three organic food constituents by itself and consider first the 
digestion of carbohydrates, next the digestion of proteins and 
then the digestion of fats. Of course, with a mixed food such 
as almost all food substances are, separate digestion does not 
take place, the entire food mass being digested more or less at 
the same time. However, as we shall find, each constituent 
is acted upon by certain digestive enzymes which act upon it 
alone, so that in order to avoid seeming confusion we shall 
treat them as separate actions. 

Digestive Region. — The digestive region in animals begins 
with the mouth and continues through the stomach and the 
small intestine, (in man practically no digestive action takes 
place in the large intestine^ The entire digestive tract, or ali- 
mentary canal, as it is termed, consists of (a) mouth, (b) esoph- 
agus, (c) stomach, (d) small intestine, (e) large intestine, with 
several contributory organs which connect with it, e.g. pan- 
creas and gall bladder. By the time the food mass reaches the 
large intestine practically all of the food capable of digestion 
has been digested and absorbed into the circulation through the 
cell membranes of the digestive tract. 



DIGESTION OF CARBOHYDRATES 

The carbohydrate food materials belong to the three classes 
of carbohydrates, viz. : 

Monosaccharoses, typified by glucose and fructose sugars ; 
Disaccharoses, typified by cane sugar, milk sugar and malt sugar ; 
Polysaccharoses not sugars, typified by starch and cellulose. 



164 ORGANIC AGRICULTURAL CHEMISTRY 

Monosaccharoses the Final Product of the Digestion of 
Carbohydrates. — The digestive action upon carbohydrates 
consists in their conversion into the final form of one of the 
three monosaccharoses, viz. glucose, fructose or galactose, CeHi 2 06. 
These simple sugars, therefore, are the only carbohydrate foods 
which do not require digestion, but are directly absorbed as they 
are. All other forms of carbohydrate food, whether soluble or 
insoluble, must be digested ; and this digestion consists in their 
conversion into one or more of the three named monosaccharoses. 
The chemical reactions involved in the conversion of the disac- 
charoses and polysaccharoses into monosaccharoses have been 
considered in the first section of our study. In the laboratory 
this conversion may be brought about by hydrolysis with dilute 
acids or alkalies. In the animal body it is always accomplished 
by the action of hydrolytic enzymes. In the chapters on carbo- 
hydrates and on enzymes these reactions have all been con- 
sidered, but it is well to review them here before we take up the 
digestive action in the animal body. 

Hydrolysis of Disaccharoses and Polysaccharoses. — All of 
the disaccharoses commonly occurring in food, viz. cane sugar, 
milk sugar and malt sugar, are hydrolyzed by particular enzymes 
into monosaccharoses as follows : 

C12H22O11 + H 2 by sucrase (invertase) -> CeH^Oe + CeH^Oe 

Cane sugar Glucose Fructose 

or sucrose 

C12H22O11 + H 2 by lactase -> CeH^Oe + CeHisOe 

Milk sugar Glucose Galactose 

or lactose 

C12H22O11 + H 2 by maltase -> 2 CeH^Os 

Malt sugar 2 Glucose 

or maltose 

The polysaccharoses, starch, dextrin and cellulose, are hydro- 
lyzed by enzymes yielding the disaccharose maltose as follows : 

2(C 6 Hi O5) J: + H 2 by ptyalin or diastase — > x C12H22O11 

Starch, cellulose (animals) (plants) Maltose 

or dextrin 



DIGESTION AND ABSORPTION 16$ 

These are the chemical reactions which occur through the 
agency of enzymes in the conversion of carbohydrate food, not 
already in the form of monosaccharoses, into this form. 

The Mouth 

Saliva, its Properties and Action. — Beginning with the 
mouth let us follow the course of the digestion of carbohydrates 
until they have all reached the assimilable form of one of the 
monosaccharoses. Digestion of carbohydrates in the mouth 
consists in the conversion of polysaccharoses into maltose by 
the action of the two enzymes, ptyalin and maltase. These 
enzymes are present in the digestive juice known as saliva. 
The saliva is secreted by glands near the mouth known as 
salivary glands, and in man amounts to about iooo to 1500 c.c. 
per twenty-four hours. The mechanical operation of mastica- 
tion causes the salivary glands to discharge into the mouth the 
juice saliva. There are several salivary glands each discharg- 
ing a saliva of somewhat different physical character. The 
drier and larger the amount of food mass the more watery is 
the saliva sent to the mouth, while a compact mass of food 
causes the flow of a juice more mucousy in its character. The 
stimulation of the salivary glands to discharge saliva may be 
brought about by a variety of means. The stimulation may be 
(a) mechanical, as is proven by the flow of saliva caused by 
putting pebbles or sand into a dog's mouth, (b) chemical, as is 
produced when a small amount of acid placed in the mouth 
causes a flow of watery saliva for the purpose of dilution or 
ejection, (c) psychical, as is produced when the mere sight of 
food causes the flow of saliva or, as the expression is, " makes 
the mouth water." In addition to these more common stimuli 
the flow of saliva may be brought about by either (d) electrical 
or (e) thermal stimulation. It is not possible to separate sharply 
these different kinds of stimulation or to determine which is 
the particular stimulation most active. In most cases where 
normal food acts, the stimulation will be a combination of 
several of those given. This stimulation of the flow of saliva 



166 ORGANIC AGRICULTURAL CHEMISTRY 

by these different stimuli typifies in general the flow of all of 
the digestive juices, which we shall presently consider. Thus 
the character of the food, the particular nature of the stimuli 
exerted and the mastication required regulate the operation of 
salivary mixing. This is because the saliva in addition to con- 
taining ptyalin and maltase, which act chemically on the starch, 
also acts in a mechanical or physical manner and enables the 
food to be swallowed or passed down the esophagus to the 
stomach; the esophagus acting merely as a connecting canal 
between the mouth and stomach. Chemically the action of 
salivary digestion is that already given of converting, by the 
action of ptyalin and maltase, all starch into maltose and this 
into glucose. This is the chief chemical reaction of the saliva 
due to the enzymes present in it. Other carbohydrate food, 
viz. the disaccharoses, cane sugar and milk sugar, and the 
monosaccharoses are not acted upon at all by the saliva. 

The ordinary saliva, which is the mixed secretion of the differ- 
ent salivary glands, is a thin, more or less sirupy or mucousy 
liquid, having a specific gravity only slightly more than that of 
water, viz. 1.005. The solid matter, therefore, in solution is 
only about 0.5 per cent. The substances present in solution in 
saliva are as follows : 

Enzymes. — The enzymes present are (a) ptyalin, converting 
starch into maltose; (b) maltase, converting maltose into glucose. 
Enzymes, capable of splitting polypeptides, the action of which 
is of only secondary importance, may also be present. 

Ptyalin and Maltase. — The complete series of changes which 
have been shown to take place when starch is digested by the 
enzymes of saliva are as follows : the starch is first converted 
from its insoluble or colloidal state into a truly soluble form 
known as soluble starch or amidulin. This soluble starch still 
gives the blue color with iodine. The soluble starch is then 
converted into dextrin, and several varieties of dextrin are suc- 
cessively produced, viz. (a) erythrodextrin, which gives a red 
color with iodine ; (b) a-, /8- and y-achroodextrins which give no 
color with iodine. Following the dextrins there are produced 



DIGESTION AND ABSORPTION 167 

iso-maltose and maltose. The iso-maltose is not formed simply 
from the y-achroodextrin, but also from each of the dextrins 
directly. The formation of maltose is the end product of the 
action of the enzyme ptyalin on starch. The action of the 
enzyme maltase, which is also present in saliva, is small in 
amount, and, as we shall see, this enzyme acts more com- 
pletely in another part of the digestive tract. 

Conditions of Salivary Action. — The action of ptyalin takes 
place in alkaline, neutral or combined acid solution. The prin- 
cipal action occurs in alkaline solution and the saliva itself is 
of slight alkaline reaction. The alkalinity of saliva is equivalent 
to about 0.1 per cent sodium carbonate, and is due to the 
presence in the saliva of di-sodium phosphate, Na 2 HP0 4 . While 
ptyalin will continue to act in somewhat strong combined 
hydrochloric acid solution, its activity is destroyed by the pres- 
ence of 0.003 t° 0.006 per cent of free hydrochloric acid. 

We should explain at this point the term combined acid. 
When protein substances react with free hydrochloric acid they 
unite with it as bases forming salts (protein salts). These 
salts ionize differently than free hydrochloric acid or such salts 
as sodium chloride, and thus act in a different way in preventing 
the action of ptyalin or as a germicide. This property will be 
referred to again when we consider the action of hydrochloric 
acid in the stomach. 

In stronger alkaline solutions than the saliva the action of 
ptyalin is inhibited but not destroyed. The action of saliva 
is better when it is somewhat diluted, to about seven times its 
volume. This fact is not in accord with the often advanced 
claim that water-drinking at mealtime is injurious to digestive 
action. 

Salts. — The second chief group of solid substances present 
in solution in saliva is that of inorganic salts. The principal 
salt present is di-sodium phosphate, Na2HP0 4 , already men- 
tioned as the cause of the alkaline reaction of saliva. The 
sodium phosphate present in saliva is the cause of the formation 
of the tartar on the teeth. With the teeth the phosphate forms 



168 ORGANIC AGRICULTURAL CHEMISTRY 

calcium phosphate which remains soluble when in the form of 
calcium acid phosphate, but is precipitated as insoluble calcium 
phosphate through the action of ammonia present in the breath. 
The tartar also contains various other constituents in addition 
to the calcium phosphate. 

Organic Substances. — In addition to the enzymes and in- 
organic salts saliva also contains several organic substances, 
viz. mucin, urea, an albumin and a globulin. The mucin is the 
most important and is the constituent which gives to saliva its 
mucilaginous character, acting as a lubricant in the passage of 
the food down the esophagus. It is a gly co-protein (see p. 
89). 

EXPERIMENT STUDY XXVII 
Saliva and Salivary Digestion 

(1) Properties, {a) Collect 25-50 c.c. of saliva on a folded filter 
paper in a funnel, and allow it to filter into a beaker or cylinder. 
Note general properties, (b) With a urinometer, specific gravity 
spindle or other form of hydrometer determine the specific gravity of 
the filtered saliva, (c) Drop a piece of red litmus paper into the 
saliva and allow to stand for some minutes. Note alkaline reaction 
to litmus, id) Make the Biuret and Millon's test for proteins (Ex- 
periment XVIII, 4, a. c) with 5 c.c. of saliva. 

(2) Isolation and Test of Mucin, (a) Pour 50 c.c. of saliva into 250 
c.c. of strong alcohol (95 %) in a tall beaker or cylinder. Allow to 
stand a day or so. Carefully decant or siphon off all but a few cubic 
centimeters of the supernatant liquid from the flocculent precipitate 
of mucin. Slowly pour the remainder of the liquid containing the 
mucin upon a small (7 cm.) filter paper in a funnel or filter through a 
Witt plate with filter paper disk on top. Wash the mucin with two 
or three small portions of alcohol and then a little ether. Remove 
paper and scrape off the collected mucin with a knife blade, and place 
it on the edge of a porous drying plate to dry. (b) After about 
fifteen minutes take one half of the mucin and divide into three por- 
tions. Make Millon's, Biuret and Xantho-proteic tests for proteins 
(Experiment XVIII, 4, a. b. c). (c) Place the other half of the mucin 
in beaker with 50 c.c. water. Add 5 c.c. of concentrated hydrochloric 



DIGESTION AND ABSORPTION 169 

acid, and boil for ten or fifteen minutes to hydrolyze the mucin. 
Neutralize the acid with sodium carbonate and then make Feh ling's 
solution test (Experiment XXII, 2), by adding 5 ex. of mixed Fehling's 
solution to the solution in the beaker and boiling again. A positive 
test for reducing sugar should be obtained. The protein and 
Fehling's solution tests prove mucin to be a conjugated glyco-protein 

(p. 89). 

(3) Action of Saliva on Starch, (a) Make up some fresh starch 
paste (Experiment XXIV, 3). (b) To 10 c.c. of this paste add an 
equal volume of water and warm to 35 C, then add 1 c.c. of saliva 
and keep mixture at 35°-4o° C. Immediately remove a drop of the 
mixture, and add to a drop of iodine on a porcelain drop plate. (The 
drop plate should be prepared first by placing a drop of iodine in 
each cavity.) If no blue color is obtained at the first test, the starch 
paste is too dilute or too much saliva has been added. At intervals 
of one minute repeat the test and follow the transformation of starch 
as given on p. 166. When no starch test is obtained with the iodine, 
test 5 c.c. of the solution with Fehling's solution. A positive test 
proves the hydrolysis of starch to maltose or glucose, (c) Repeat 
(b) , adding before the saliva o. 1 c.c. of concentrated acid. This amount 
of acid makes the solution approximately 0.3 per cent acid. Note 
the effect of the acid on the action of the saliva enzymes. 

The Stomach 
In the stomach the only carbohydrate digestion which takes 
place is the continuation of the action of ptyalin which began 
in the mouth. As we shall find when we consider protein diges- 
tion, the stomach juice has an acidity of about 0.2 to 0.3 per 
cent free hydrochloric acid. This is far above the limits of 
acidity destructive to ptyalin which we have just given as 
0.003 t0 0.006 per cent. While the stomach juice has this high 
acidity the food mass on entering the stomach does not reach 
this acidity for a considerable length of time. It rests in the 
front or cardiac end of the stomach for a period of time vary- 
ing from one half to two hours before its acidity reaches the 
limit of 0.003 P er cent which destroys the action of ptyalin. 
Within this time salivary digestion of carbohydrates continues 
in the stomach and ceases when the limit of acidity is reached. 



170 ORGANIC AGRICULTURAL CHEMISTRY 



The Small Intestine 

The digestion of carbohydrate food beginning in the mouth 
and ceasing in the stomach is taken up again when the food 
reaches the small intestine. The action of the salivary enzymes 
has been completely destroyed, and the action which is taken 
up again in the small intestine is due to new enzymes. 

Pancreatic Juice. Amylopsin. — The first enzyme acting on 
carbohydrate food in the intestine is the starch-hydrolyzing 
enzyme amylopsin. This enzyme is present in the pancreatic 
juice which flows into the intestine from the pancreas very near 
the opening from the stomach into the intestine. The action 
of amylopsin is exactly like that of ptyalin, i.e. it hydrolyzes 
starch to maltose through the intermediate stages of dextrin 
and iso-maltose. It is, however, more active than ptyalin. 
The pancreatic juice is like the saliva in being alkaline in re- 
action and the amylopsin, like ptyalin, acts best in this medium. 
Any starch or dextrin food which is undigested by the action 
of ptyalin of the saliva is acted upon in the intestine by the 
amylopsin and the resulting product is maltose. Thus, when 
the carbohydrate food materials have been acted upon by both 
ptyalin and amylopsin, it contains only the following sub- 
stances: (a) monosaccharoses, originally present in the food, 
and some glucose formed from maltose by the action of maltase 
in the saliva, (b) disaccharoses, cane sugar and milk sugar, 
originally present in the food and malt sugar in the food or 
formed from polysaccharoses by the action of ptyalin and 
amylopsin. The monosaccharoses now present in the food 
mass need no further digestion. The disaccharoses, however, 
all need to be hydrolyzed to monosaccharoses before digestion 
is complete. It is interesting to note that amylopsin is not 
present in the pancreatic juice of infants for the first few weeks 
after birth, which explains their inability to digest starch. 

Intestinal Juice. — The hydrolysis of the three disaccharoses 
is accomplished by three enzymes which are present in the 
intestinal juice secreted by the cells of the mucous lining of the 



DIGESTION AND ABSORPTION 171 

small intestine and by them discharged upon the food mass at 
about the same time or very soon after it has been mixed with 
the pancreatic juice. These two digestive juices act more or 
less together upon the food mass. The intestinal juice is also 
termed succus entericus. 

The three enzymes of the intestinal juice which hydrolyze 
disaccharoses are : 
Sucrase or invertase, which hydrolyzes cane sugar (sucrose) 

to glucose and fructose. 
Maltase, which hydrolyzes malt sugar (maltose) to glucose. 
Lactase, which hydrolyzes milk sugar (lactose) to glucose 
and galactose. 

The intestinal juice is alkaline to methyl orange and con- 
tains no free hydrochloric or other strong acid. The enzymes 
present act in media of this reaction. 

The digestion of carbohydrate food is now completed and the 
final products are glucose, fructose and galactose : the three most 
common monosaccharoses. These three are all diffusible 
through the cellular membranes of the digestive tract and as 
such they pass into the circulatory system ready to take up 
the metabolic changes by which they form body substance or 
yield energy. 

DIGESTION OF PROTEINS 

The protein food of animals may consist of either animal or 
vegetable proteins or both. These different proteins are alike 
in most respects, and any difference in them shows itself mainly 
in the products of digestion and does not concern the digestive 
process itself. The digestive enzymes acting upon protein 
food act alike, so far as we know, on both classes. 

The chemical changes occurring in the digestion of protein 
food are analogous to those that take place with carbohydrates, 
i.e. they are hydrolytic. In the laboratory proteins may be 
hydrolyzed by boiling with acids or alkalies and the products 
obtained are eventually amino-acids such as glycine (amino- 
acetic acid), etc. This same hydrolysis of proteins may be 



172 ORGANIC AGRICULTURAL CHEMISTRY 

brought about by enzymes, but in such actions several inter- 
mediate products have been isolated, known as proteoses, 
peptones and polypeptides. In the classification of proteins 
these are termed secondary derived proteins as they still possess 
certain protein characters. The final products of both acid 
and enzyme hydrolysis, the amino-acids, are definite nonprotein 
compounds. 

The Stomach 

The digestion of protein food begins in the stomach, prac- 
tically no digestion of these food constituents taking place in 
the mouth, by the action of salivary enzymes. The protein 
digestion in the stomach is brought about by the action of two 
enzymes, gastric rennin and pepsin, both contained in the 
stomach juice known as gastric juice. 

Gastric Juice. — The gastric juice is secreted by two sets of 
gastric glands present in two regions of the mucous lining of 
the stomach, and flows into the stomach when certain stimu- 
lation occurs. This stimulation is usually either chemical, 
due to the character of the food mass, such as presence of water, 
milk or food juices, or psychical, due to the psychic influence of 
sight, thought or taste of food. It has been found that water 
in the stomach stimulates the flow of gastric juice and that 
water taken at mealtimes is beneficial rather than injurious 
to the action of gastric digestion. This agrees also with the 
fact previously referred to in connection with the influence of 
water upon the action of salivary digestion. 

Gastric juice is a thin liquid varying considerably in specific 
gravity from i.ooi to 1,010. It contains from 2 to 3 per cent 
of solid matter. The chief substances present in gastric juice 
are enzymes, free hydrochloric acid and inorganic salts. The 
distinctive property of gastric juice is its acidity due to the 
free hydrochloric acid, and equaling 0.2 to 0.3 per cent. 

Enzymes. — The enzymes found in gastric juice are of three 
classes, two of which act upon proteins and one, gastric lipase, 
acts upon fats. The protein enzymes are : 



DIGESTION AND ABSORPTION 173 

Gastric Rennin. — This enzyme is not a protein-hydrolyzing 
enzyme, but a protein-coagulating enzyme. It acts upon milk 
caseinogen, the form of casein present in milk, and converts 
it into soluble casein and a proteose body. The soluble casein 
reacts with calcium salts forming calcium casein or true casein, 
which is insoluble and is precipitated as a curd or coagulum. 
Gastric rennin acts best in acid media equal to the acidity of 
gastric juice. 

Pepsin. — The most important enzyme of the gastric juice 
is pepsin, which is a true protein-hydrolyzing or proteolytic 
enzyme. The enzyme does not occur as such in the cells 
where it is secreted, but is present there in the form of its 
mother substance or zymogen, known as pepsinogen. Pepsin- 
ogen is activated or converted into pepsin enzyme by the action 
of the free hydrochloric acid present in the gastric juice. Pepsin 
acts best in acid media, the amount of acidity varying with the 
character of the protein to be hydrolyzed. Fibrin protein is 
digested better by pepsin when the acidity is 0.08 to 0.10 per 
cent, while coagulated egg albumen requires an acidity of 0.25 
per cent. The hydrolysis of protein by means of the enzyme 
pepsin yields as products not only the derived proteins, pro- 
teoses and peptones, but also amino-acids. It is probable that 
in the stomach, however, the derived proteins, proteoses and 
peptones are the chief hydrolytic products varying more or 
less with the character of the protein food. Therefore, when 
the protein food has passed through the stomach, it is more or 
less completely converted into proteoses and peptones with some 
amino-acids and some unhydrolyzed protein. 

Hydrochloric Acid. — As has been stated the distinctive 
character of gastric juice is its relatively strong acidity, 0.2 to 
0.3 per cent, due to the presence of free hydrochloric acid. 
The origin of this hydrochloric acid is not well established, but 
it is probably derived from the chlorides, principally sodium 
chloride, present in the blood and may be produced by elec- 
trolytic action or by the action of the lactic acid which is also 
present. 



174 ORGANIC AGRICULTURAL CHEMISTRY 

The function of hydrochloric acid in the gastric juice is also 
somewhat in doubt. It is probably not, as has been supposed, 
to assist in the hydrolysis of the protein, though the action of 
pepsin itself is best in acid solution. Its most important func- 
tion is probably that of a germicide to prevent the action of 
putrefying bacteria. It has been found that hydrochloric 
acid of approximately the same strength as that found in the 
gastric juice acts best as a germicide. We have stated that 
free hydrochloric acid of much less strength, viz. 0.003 to 
0.006 per cent, destroys the activity of ptyalin. When, how- 
ever, the free hydrochloric acid reacts with protein it forms 
protein salts, or, as it is then termed, combined hydrochloric acid. 
This combined acid is not nearly so effective as a germicide 
as the free acid. The food mass as it comes from the mouth 
remains for some time below 0.003 per cent acidity as the acid 
in the gastric juice first combines with the protein and only 
gradually exerts an influence as free acid, thus destroying 
ptyalin action. Eventually the whole food mass becomes 
saturated with free acid of about 0.2 per cent and is rendered 
germ-resistant while the action of ptyalin is destroyed. 

EXPERIMENT STUDY XXVIII 
Gastric Digestion 

(1) Action of Pepsin (a) Preparation of Egg Albumen. Cut some 
glass tubing of small diameter (2-3 mm.), in twelve-inch lengths. 
Using a tube as a pipette, suck it one half full of fresh egg albumen. 
Holding the finger over the mouth end, insert the portion containing 
the albumen into a beaker full of water at 8o°-9o° C, keeping the 
finger over the end until the albumen has coagulated. Heat the 
water to ioo° and allow the tube to remain in the water until the 
albumen is thoroughly coagulated. Prepare several tubes in this 
way. When the albumen is all hard remove the tubes from the 
water and with a sharp file scratch and break the tube containing 
coagulated albumen into one half or one fourth inch lengths. 
These sections of tubing containing coagulated albumen are now 
used as test pieces for studying the action of pepsin, (b) Prepare 



DIGESTION AND ABSORPTION 175 

a 10 per cent water solution of commercial pepsin and an approxi- 
mate 0.5 per cent solution of hydrochloric acid made by adding 1.5 
c.c. concentrated HC1 to 100 c.c. water, (c) Take four test tubes and 
place in (1) 5 c.c. pepsin solution + 5 c.c. water (neutral). In tube 
(2) 5 c.c. pepsin solution + 5 c.c. 0.5 per cent hydrochloric acid solu- 
tion (approximately 0.25 per cent acid). In tube (3) 5 c.c. pepsin 
solution + 5 c.c. of 0.5 per cent sodium carbonate solution. Into 
each test tube now place a test section of coagulated egg albumen. 
Put the tubes in an incubator at 38 C. or in a beaker of water kept 
at 38°-40° C, and let them remain for an hour or more, noting any 
changes in the albumen. Digestion takes place only in tube (2). 
(d) If desired make similar tests diluting the acid so as to make solu- 
tions containing 0.2 per cent acid, 0.1 per cent acid and another to 
which 1.0 c.c. of concentrated hydrochloric acid has been added. 
Note most favorable acidity, (e) Repeat also with three tubes made 
as tube (2) in (b), keeping one at room temperature, one at 38°-40° C, 
one heated to ioo° C. in boiling water, and another immersed in cold 
water io°-is° C. Note at which temperature digestion is most 
active. Warm the first and last of these tubes to 38°-4o° C. and note 
result. Cool the one heated to boiling down to 38°-40° C. and note 
result. Low temperatures inhibit the action of pepsin but do not 
destroy the enzyme. Boiling temperature destroys the enzyme 
completely. 

(2) Action of Rennin. Use a commercial rennet obtained from a 
dairy laboratory or dissolve a rennet tablet in ia-20 c.c. water. Warm 
100 c.c. of whole milk to 38°-4o° C. and add 2 or 3 drops of the rennet 
solution. Mix slightly and then allow to stand. Note coagulation 
of milk casein. When a good coagulation has formed, break it up 
with a glass rod; decant off the whey and collect the casein on a 
folded filter paper. Press as dry as possible and test a portion of the 
casein for protein by Millon's or Xantho-proteic test (Experiment 
XVIII, 4, a. b). Compare with Experiment XXIX. 

The Small Intestine 

The most important protein digestion takes place in the 
small intestine by the action of several enzymes present in 
two digestive juices, viz. pancreatic juice, secreted by the 
pancreas, and intestinal juice, secreted by the cells of the mucous 



176 ORGANIC AGRICULTURAL CHEMISTRY 

lining of the small intestine. Although we shall consider these 
two digestive juices and the action of their enzymes separately, 
they act more or less together. 

The chemical reactions taking place when protein food is 
hydrolyzed by the enzymes of these two juices are of the same 
nature as those occurring with pepsin, i.e. the protein is hydro- 
lyzed to amino-acids as the final product. 

Pancreatic Juice. — The pancreatic juice is secreted by the 
pancreas, a contributory organ which is connected with the 
small intestine by a duct known as the duct of Wirzung. This 
duct opens into the small intestine near the opening from the 
stomach to the intestine. This opening is known as the pylorus. 

Hormones. — The secretion of the pancreatic juice and its 
flow into the intestine for the purpose of digesting the protein 
food, which comes from the stomach, is an exceedingly interest- 
ing process involving the action of a new class of substances 
known as hormones. These hormones are similar to enzymes 
in some respects, but are not destroyed by boiling. In the 
case of the relation of hormones to pancreatic juice the series 
of actions has been very thoroughly established, and it will 
be worth our while to consider them carefully. 

When the food mass has been thoroughly mixed in the stomach 
by means of the peristaltic action of the stomach muscles, it is 
finally passed along to the pyloric region of the stomach, where 
it remains until its acidity reaches a certain point. In this 
condition the food mass is known as chyme. The opening of 
the pylorus and the actual passage of the chyme through it 
is regulated by the acidity of the chyme. When this condition 
is reached the pylorus opens and the chyme enters the small 
intestine, which, for the length of about twelve inches, is known 
as the duodenum (the name signifies twelve). Into this duo- 
denum the duct of Wirzung opens. In the epithelial cells of 
the lining of the duodenum is a substance or hormone known 
as prosecretin. The hydrochloric acid of the chyme hydrolyzes 
this prosecretin and yields a second hormone known as secretin. 
This hormone secretin is then conveyed by the blood to the 



DIGESTION AND ABSORPTION 177 

pancreas where it acts as a stimulus causing the flow of pan- 
creatic juice. 

The pancreatic juice then passes from the pancreas through 
the duct of Wirzung to the duodenum. It is a colorless alkaline 
solution amounting in twenty-four hours to about 650 c.c. in 
man. It has a specific gravity of about 1.008 and contains 
about 1.3 per cent solid matter. 

Enzymes. — The most important constituents of the pan- 
creatic juice are the enzymes. These enzymes are of three 
classes, (a) amylolytic or starch-hydrolyzing, viz. amylopsin, 
which we have already considered, (b) protein enzymes, viz. a 
protein-coagulating enzyme, pancreatic rennin, similar to gastric 
rennin, and a protein-hydrolyzing enzyme known as trypsin, 
resembling pepsin, (c) a fat-hydrolyzing enzyme which we shall 
consider later. 

( Rennin. — The enzyme pancreatic rennin, present in the 
pancreatic juice, acts exactly like gastric rennin of the gastric 
juice, coagulating the caseinogen of milk. 

Trypsin. — The most important enzyme of the pancreatic 
juice is the proteolytic enzyme trypsin. This enzyme, like 
pepsin, does not exist in the digestive juice as the enzyme it- 
self, but as the mother substance or zymogen known in this case 
as trypsinogen. When the pancreatic juice reaches the intestine, 
it is unable to hydrolyze protein as has been shown by drawing 
off the pancreatic juice from the pancreas by means of a fistular 
opening. In order that the trypsinogen present in the pan- 
creatic juice may become active by conversion into trypsin it 
must be activated by another enzyme which is present in the 
intestinal juice and known as enterokinase. This substance is 
probably an enzyme though differing from them in a certain 
particular in that it seems to act quantitatively upon a definite 
amount of trypsinogen. It is also found to be present in the 
intestinal juice only when pancreatic juice is present. When, 
therefore, pancreatic juice containing trypsinogen becomes 
mixed with intestinal juice, the enterokinase of the latter acti- 
vates the trypsinogen and the enzyme trypsin is produced. 



178 ORGANIC AGRICULTURAL CHEMISTRY 

This shows why it is always necessary for the pancreatic juice 
and intestinal juice to act together in the same region and on 
the same food mass. 

The hydrolytic action of trypsin takes place in alkaline 
solutions and is similar to that of pepsin in its chemical nature. 
It differs, however, in the end products of the hydrolysis. 
While pepsin hydrolysis of proteins yields mostly derived 
proteins, proteoses, peptones and polypeptides with a small 
amount of amino-acids, the action of trypsin yields mostly 
amino-acids and only small amounts of the derived proteins. 
Trypsin may produce the amino-acids from either original 
protein or from derived protein. The final result then of the 
action of the enzymes of the pancreatic juice upon protein food 
is to convert them largely into the final end products, amino- 
acids. 

It should also be mentioned that according to some authori- 
ties trypsinogen may be activated by calcium salts, while others 
claim that trypsin is formed by the action of calcium salts 
upon another zymogen than trypsinogen. 

Intestinal Juice. Erepsin. — The juice secreted by the epi- 
thelial cells of the small intestine and known also as succus enteri- 
cus contains another enzyme connected with the digestion of pro- 
teins in addition to the enterokinase just mentioned. This is 
the proteolytic enzyme erepsin. Erepsin differs from the two 
proteolytic enzymes thus far considered in that its action is 
almost wholly upon the derived proteins ; proteoses, peptones 
and polypeptides. These compounds are present after protein 
food has been acted upon by pepsin and trypsin, and they are 
hydrolyzed by erepsin to the final end products, amino-acids. 
Erepsin does possess the power of hydrolyzing a few original 
proteins, viz. caseinogen of milk and protamines and histones. 

This completes, therefore, the digestion of protein food, which 
by the combined and supplementary action of the three pro- 
teolytic enzymes, pepsin of the gastric juice, trypsin of the 
pancreatic juice and erepsin of the intestinal juice, are hydrolyzed 
to the final end products, amino-acids. The protein food is 



DIGESTION AND ABSORPTION 179 

thus converted into soluble and diffusible forms, and is in a 
condition ready for absorption through the digestive, tract into 
the circulation. It must not be concluded, however, that no 
absorption of the products of protein digestion takes place until 
the intestinal juice has acted upon the food mass. As will be 
shown later when the absorption of the products of digestion 
is considered, this process is a gradual and continual one almost 
from the beginning of the digestive action. 

DIGESTION OF FATS 

We now come to the consideration of the digestion of the 
third of the three essential food constituents, viz. fats. 

Fat food consists of both animal and vegetable fats and oils 
which may be treated as one in connection with the processes 
of digestion. The difference between the different fats and 
oils consists in different physical properties, or different forms 
in which they may be present in the food, e.g. as free globules 
of fat, or in the form of an emulsion as in milk. The difference 
in chemical composition of the fats and oils used as food con- 
sists in the different fatty acids which are present in combina- 
tion. It will be recalled that fats and oils are esters or ethereal 
salts of glycerol and a certain few of the fatty acids, especially 
butyric, caproic, lauric, myristic, palmitic, stearic of the satu- 
rated series, and the unsaturated acid oleic and sometimes 
linolic. The metabolism of fats is somewhat dependent upon 
the character of the fatty acid present, but the process of 
digestion is the same for all. 

Hydrolysis of Fats. — The digestion of fats consists, chemi- 
cally, simply in the hydrolysis of the glycerol ester into glycerol 
and the fatty acid as represented by the following equation : 

CH 2 OOCCi 5 H 3 i CH2OH 

I I 

CHOOCC15H31 + 3 H 2 -> CHOH + 3 C 15 H 3 iCOOH 

CH 2 OOCCi 5 H8i CH2OH 

Glyceryl tri-palmitat* Glycerol Palmitic acid 



180 ORGANIC AGRICULTURAL CHEMISTRY 

This reaction is brought about in the digestive tract by means 
of fat-hydrolyzing enzymes known by the general name of 
lipolytic enzymes or lipases. It is well to consider the striking 
fact that all of the digestive reactions of either carbohydrates, 
proteins or fats are reactions of hydrolysis. The actions are all 
brought about by means of enzymes, and digestive enzymes are 
all hydrolytic. This statement has one exception if the enzymes 
gastric rennin and pancreatic rennin are classed as digestive. 
These two enzymes are coagulating enzymes, and, as they may 
be considered as simply preparing the proteins for the real 
action of digestion, they may be classed in a different group 
than the true digestive enzymes. 

The Stomach 

Gastric Lipase. — Digestion of fats like that of proteins 
begins in the stomach. In the gastric juice, in addition to the 
enzymes already mentioned which produce protein hydrolysis, 
there is present a lipolytic or fat-hydrolyzing enzyme known 
as gastric lipase. This enzyme acts best in neutral solutions, 
so that under normal conditions of stomach acidity its action 
is not great, and the larger part of fat digestion is deferred till 
later. The gastric lipase also acts best on emulsified fat, and 
fat not so emulsified is very little, if at all, digested in the 
stomach. In milk the fat is in the form of an emulsion and 
this is also true in the yolk of eggs. In both of these cases in 
man a large part of the fat digestion (78 per cent in egg yolk) 
occurs in the stomach. On this account infants, before the 
pancreatic juice is developed, are able to digest milk and egg 
yolk. 

The Small Intestine 

Pancreatic Lipase. — The chief fat digestion takes place in 
the small intestine due to the action of a fat-hydrolyzing enzyme 
present in the pancreatic juice. This enzyme is known as 
pancreatic lipase or as steapsin. The enzyme acts in alkaline 



DIGESTION AND ABSORPTION 181 

solution and is, therefore, in a favorable medium in the small 
intestine. 

As a result then of the digestion of fat by the gastric and 
pancreatic lipases (mostly the latter) the fat of the food is 
hydrolyzed into glycerol and fatty acids. The glycerol is 
soluble in water and is diffusible through the cell membranes. 
The free fatty acids are, however, practically insoluble in 
water and are nondiffusible through the cell walls. They 
become soluble and diffusible by reacting with the alkalies of 
the pancreatic juice with the formation of alkali salts of the 
fatty acids. These alkali salts of the fatty acids are, it will be 
recalled, soaps. Soaps have the property of forming emulsions 
with fats, and in the form of such an emulsion fats are diffusible 
through the cell membranes. Fats are thus rendered diffusible 
in two ways, (i) By a true process of digestion consisting of 
hydrolysis into glycerol and fatty acids and the subsequent 
formation of soluble salts of the acids by means of alkalies 
present in the digestive juices. (2) By the formation of an 
emulsion of unchanged fat with the soaps formed as a result 
of the first process. In both of these resulting forms, i.e. 
alkali salts of fatty acids or soaps and emulsions of free fats, 
the fat food is absorbed through the cell walls of the digestive 
tract and enters the circulation. 

The Bile 

There still remains one more digestive liquid to consider, 
which, while it contains no digestive enzymes, assists in the 
digestion of food constituents, especially the fats. The bile is a 
secretion of the liver, from which it passes to the gall bladder, 
which acts as a reservoir, and thence through the bile duct 
to the small intestine joining with the duct of Wirzung, which 
brings the pancreatic juice. The bile, therefore, mixes with 
the pancreatic juice and it is here that it assists in the digestion 
of the fats. 

Its first action is probably one in which it acts as a stimulator 
of the steapsin of the pancreatic juice. This stimulation re- 



182 ORGANIC AGRICULTURAL CHEMISTRY 

action appears to rest in constituents of the bile known as bile 
salts. These salts are usually sodium salts of two acids, glyco- 
cholic and taurocholic acids, which are so-called conjugated acids 
of glycocoll or glycine and cholic acid in the case of glycocholic 
acid, and taurine and cholic acid in taurocholic acid. Cholic 
acid itself is a complex acid probably monobasic, but of un- 
determined constitution. 

The second way in which the bile assists in the digestion of 
fats is in the formation of soaps and emulsions. Bile is alkaline 
in reaction and the alkalies present unite with the free fatty 
acids formed by the hydrolysis of the fats, and the result is soap. 
These soaps or alkali salts of the fatty acids are probably 
directly absorbed through the cell membranes. The emulsify- 
ing power of bile may be due in part to the formation of these 
soaps, but it is also a function of the bile itself. When bile 
alone is mixed with pure fat, the fat is emulsified and can then 
diffuse through cell membranes. In these two ways, then, by a 
stimulation of the lipolytic enzyme of pancreatic juice, and by 
the formation of soaps and emulsions, the bile assists in the 
pancreatic digestion and absorption of fats. 

The secretion of bile and its flow into the intestine is de- 
pendent upon the presence in the intestine of undigested fat 
food and probably also of protein food, and it seems to be regu- 
lated by the same or similar hormones as were described in 
connection with the flow of pancreatic juice. 

Bile is a viscous alkaline liquid of specific gravity, i.oi to 
1.04. It is of various colors, mostly yellow, green or brown, 
and has a bitter taste. The amount secreted daily varies 
between 500 and 1100 c.c. per day for man. 

The Large Intestine 

It was previously stated that, in man, no digestion occurs in 
the large intestine. This is true so far as new digestive pro- 
cesses or the secretion of juices containing digestive enzymes 
are concerned. No digestive juices containing enzymes are 
secreted in the large intestine. A continuation of digestive 



DIGESTION AND ABSORPTION 183 

processes begun in the small intestine may take place for some 
time in the upper portion of the large intestine. The greater 
part of the digestion of food material is, however, completed 
by the time the food mass enters the large intestine. 

ABSORPTION OF FOOD 

The absorption of food, or more exactly of the end products 
of food digestion, takes place more or less continually from the 
time the food mass reaches the stomach until it has passed 
through the small intestine and into the large intestine. This 
absorption process is one of diffusion through the cell mem- 
branes lining the digestive tract. It has been found, however, 
that the process is not one of simple diffusion through mem- 
branes in accordance with physico-chemical laws, but that 
it takes place much more rapidly than can be explained by such 
laws. On this account the process has been termed resorption 
rather than absorption. We shall, however, use the more 
common term, viz. absorption. 

Carbohydrates. — The carbohydrate food converted by the 
process of digestion into the three monosaccharoses, glucose, 
fructose and galactose, is not absorbed through the cell mem- 
branes of the digestive tract until it reaches the small intestine. 
At this point, when the digestion is practically complete, absorp- 
tion occurs and the monosaccharoses pass through the cell 
walls of the intestine and enter the capillary blood vessels in 
the wall of the intestine and then pass into the portal vein 
leading to the liver. The blood present in the portal vein 
always contains a large amount of these monosaccharoses, 
principally glucose, though both fructose and galactose may 
be present. After the food mass leaves the small intestine, any 
digested carbohydrate material remaining is absorbed through 
the walls of the large intestine and reaches the same destina- 
tion. It has been found, however, that less than 10 per cent of 
digested carbohydrate food remains unabsorbed when the food 
leaves the small intestine. Carbohydrate food, therefore, after 
digestion reaches the circulation in the portal vein leading to 



1 84 ORGANIC AGRICULTURAL CHEMISTRY 

the liver in the form of the three common monosaccharoses, 
though mostly in that of glucose. It is claimed by some au- 
thorities that absorption of carbohydrates does take place in 
the stomach, but if so it is probably only in a limited amount 
or under special conditions. When such absorption does occur, 
the products reach the portal vein as just described. 

Proteins. — While some absorption of protein digestion 
products may occur in the stomach, yet with these food ma- 
terials, as with carbohydrates, the chief absorption of the 
products takes place in the small intestine and is completed 
in the upper part of the large intestine. More than 90 per 
cent of the digested protein is, however, absorbed before the 
food mass reaches the large intestine. 

We have shown that the final products of protein digestion 
are amino-acids, and that the hydrolysis of proteins yielding 
these products takes place in the small intestine due to the 
combined action of the pancreatic enzyme trypsin and the 
intestinal enzyme erepsin. While gastric digestion in the 
stomach begins with original proteins and ends almost wholly 
with derived proteins; peptones, and proteoses, the tryptic 
digestion beginning at the same point, i.e. with original pro- 
tein, carries the hydrolysis through to amino-acids. Erepsin 
cannot begin with original proteins, but takes the derived pro- 
teins from uncompleted gastric and tryptic digestion and com- 
pletes the hydrolysis to the final stage of amino-acids. 

It has been difficult to determine whether absorption of 
digested protein food takes place with the final end products 
only or with the derived proteins as well. The presence of 
erepsin, which has without doubt an essential action in protein 
digestion, as supplementing the action of both pepsin and 
trypsin, would seem to indicate that it is necessary for absorp- 
tion that protein food be completely hydrolyzed to amino-acids. 
It has long been considered as a fact, however, that amino- 
acids alone when fed to animals or when injected into the blood 
are unable to be used by the animal to synthesize body protein. 
If, however, a polypeptide nucleus is present, the amino-acids 



DIGESTION AND ABSORPTION 185 

may be utilized. It is possible that this polypeptide nucleus 
may be present in the blood as a result of the tearing down of 
body protein, and that it may not be necessary for it to have 
been absorbed from the protein digestion products of the diges- 
tive tract. If polypeptide material is absorbed for the later 
synthesis of body protein, it would seem to be probable that 
the stomach as a digestive organ is of primary importance, 
and that considerable absorption of digestion products would 
occur before the food mass was further digested. The evidence 
has lately gone to show, however, that the digestive function of 
the stomach is of secondary importance and of almost no es- 
sential character ; the essential digestion and absorption taking 
place later after the small intestine is reached. It has been 
shown, too, that almost immediately, even in the cell wall of 
the small intestine, resynthesis of protein material takes place. 
We can only say then that while it may be true that absorption 
of protein digestion products is all in the form of amino-acids, 
yet it is not fully established, and polypeptide groups may also 
be absorbed. 

In the end the digestion products are found immediately 
after absorption in the intestinal wall, and are thence conducted 
to the portal vein, where both amino-acids and derived protein 
groups are present. 

Fats. — The absorption of fats takes place in two forms as 
has been indicated, viz. as salts (soaps) of the fatty acid formed 
through the reaction of the bile and intestinal alkalies with the 
free acid resulting from the fat hydrolysis, and in the form of 
emulsions produced directly by the bile or by the soaps pre- 
viously formed. The fat thus absorbed is collected first in the 
lymphatic circulatory system, and from that reaches the blood. 
Like the proteins, the fats if absorbed wholly as hydrolyzed 
products and not as free fat (in emulsion), are immediately in 
the intestinal wall resynthesized to fat. The question of 
whether free unchanged fat is directly absorbed is still open, 
but the experiments with hogs fed with cottonseed oil, in which 
the lard shows positive proof of the presence of cottonseed oil, 



1 86 ORGANIC AGRICULTURAL CHEMISTRY 

goes to show that the absorption may be direct. If not, the 
resynthesis of the fat from the hydrolytic products must be 
immediate and must yield the same original fat as is fed in the 
food. The fact should be mentioned that lipolytic enzymes 
which bring about the hydrolysis of fats may also assist in their 
resynthesis, as it has been shown that these enzymes primarily 
possess the power of reversibility, i.e. of producing the reverse 
reaction. 

RESUME OF DIGESTION AND ABSORPTION 

Before taking up the study of metabolism let us review in 
outline the course of food through the digestive tract and its 
absorption into the circulatory system, i.e. the blood. 

Mouth. — In the mouth ptyalin present in the saliva hydro- 
lyzes starch and dextrin to maltose and some maltose may be 
further hydrolyzed to glucose by maltase also present. The 
food then passes down the esophagus to the 

Stomach, where it remains for a short period (one half to 
two hours) still alkaline from the action of saliva and where 
ptyalin still continues to work. Eventually the peristaltic 
movements of the muscular lining of the stomach mix the 
food mass with the acid gastric juice and the food mass passes 
slowly from the cardiac or front end of the stomach through to 
the rear or pyloric end. As the food mass becomes acid through 
the action of the free hydrochloric acid of the gastric juice the 
action of ptyalin and maltase is completely stopped, the enzymes 
being killed. The free acid of the gastric juice acts as a germi- 
cide preventing bacterial putrefaction, and produces an acid 
medium in which the pepsin of the gastric juice can best act. 
In the gastric juice gastric rennin coagulates the milk caseinogen 
preparing it for digestion. Pepsin hydrolyzes protein food 
to peptones, proteoses, polypeptides and a small amount of 
amino-acids. Gastric lipase hydrolyzes fats, almost wholly 
those in the form of emulsions, to glycerol and fatty acids. In 
the stomach some absorption may take place, though probably 
small in amount. 



DIGESTION AND ABSORPTION 187 

Intestines. — The acid condition of the food mass (chyme) 
regulates the passage of the mass through the pylorus, the 
opening from the stomach to the small intestine, the first twelve 
inches of which is known as the duodenum. In the duodenum, a 
few inches from the pylorus, the duct of Wirzung, leading from 
the pancreas, together with the common bile duct from the 
gall bladder, unite in a common opening. Due to the action 
of the free hydrochloric acid of the chyme food mass a hormone, 
prosecretin, produced by the cell walls of the small intestine, 
yields another hormone, secretin, which is then conveyed by the 
blood to the pancreas. In the pancreas the secretin stimulates 
the flow of pancreatic juice, which then flows down the duct of 
Wirzung, unites with the bile from the gall bladder and together 
they enter the small intestine. The intestinal juice, succus 
entericus, secreted by the cells of the small intestine, also mixes 
with the pancreatic juice and the bile, and the three act to- 
gether in the complete intestinal digestion. These juices are 
all alkaline and neutralize the acid reaction of the chyme. The 
amylolytic enzyme, amylopsin, of the pancreatic juice hydrolyzes 
any undigested starch or dextrin to maltose, and then by the 
combined action of the three disaccharose-hydrolyzing enzymes, 
sucrase, maltase and lactase, present in the intestinal juice, 
all carbohydrate food is hydrolyzed to the final end products 
viz. glucose, fructose and galactose. In this form the carbo- 
hydrate food is absorbed through the intestinal wall into the 
blood capillaries, and enters the portal vein where they may all 
three be found. Glucose is, however, the chief one of the three. 
The pancreatic juice contains the zymogen, trypsinogen, which 
is activated by an enzyme, enterokinase, of the intestinal juice, 
yielding the active enzyme, trypsin. Trypsin is a proteolytic 
enzyme and hydrolyzes unchanged protein mostly to amino- 
acids but yielding also polypeptides, peptones and proteoses. 
Following this in its action on protein food the enzyme, erepsin, 
of the intestinal juice acts upon the derived proteins (peptones, 
proteoses and polypeptides) converting them all by hydrolysis 
into amino-acids. While some absorption of digestion products 



i8S ORGANIC AGRICULTURAL CHEMISTRY 

may take place in the stomach, it is mostly accomplished in the 
small intestine and approximately 90 per cent of the digested 
food is absorbed here before the food mass passes on to the 
large intestine. The protein digestion products are absorbed 
into the blood capillaries and, like the carbohydrate products, 
enter the portal vein. 

The fats are hydrolyzed by pancreatic lipase, steapsin, into 
glycerol and fatty acids. The fatty acids are converted into 
soluble, diffusible soaps by the alkalies of the bile and intestinal 
juice. These soaps are diffusible and are absorbed through the 
cell walls, entering the lymphatic circulation and thence pass- 
ing into the blood. Fats are also emulsified by the direct 
action of the bile and also of the soaps just mentioned. The 
bile also acts as a stimulator of the steapsin. In the large in- 
testine there are no enzymes secreted, and, in man, the only 
digestion occurring takes place in the upper end, and is the 
simple gradual completion of the digestive processes already 
mentioned. Absorption of digestion products takes place in 
the large intestine to some extent, but amounts to less than 10 
per cent of the digested food material. The absorbed material 
here follows the same course as that previously absorbed from 
the small intestine. 

TIME FOR FOOD PASSAGE 

The length of time required for food to be completely digested 
varies considerably, as would be expected. Small test meals 
have been known to pass through the stomach in one to four 
hours, while large meals of meat have required twelve hours. 
In man the average time is about seven hours for small meals. 
For the food mass to pass the ileocecal valve, between the 
small intestine and the large, requires about nine to twenty- 
three hours from the time of eating. The three food con- 
stituents when fed separately pass through the digestive tract 
with different speeds. Carbohydrates are the most rapid, 
requiring about four hours, fat about five hours, and protein 



DIGESTION AND ABSORPTION 189 

about six hours from the time of feeding until the first food 
passes into the large intestine. These data refer to experi- 
ments with cats. When mixed, as in ordinary food, each 
constituent has the effect of either retarding or hastening the 
passage of the other constituents. In the large intestine the 
residual food mass remains for a considerable time, usually 
for one to two days or even longer. 



CHAPTER XII 

ANIMAL FOOD AND NUTRITION {Continued) 
METABOLISM 

We have emphasized the fact that the distinctive character 
of animals as compared with plants is that they are predomi- 
nantly energy-liberating organisms. The energy is stored up 
in complex compounds and the tearing down of these com- 
pounds by oxidation sets free the energy contained in them. 
We have also given as a definition that any substance which is 
used by the animal to build up body substance or to yield 
energy is a food. Body substance in this connection means 
not only cell substance and muscular tissue, essentially protein 
in composition, and body fat, but also any substance more 
complex than the absorbed food material. Such substances 
may be reserve or stored, or they may be transition material 
on the way to still more complex forms. 

The food substances which we have been considering and 
which we have followed through their absorption into the 
animal circulation are, therefore, to undergo further change, 
and this change probably always occurs within the living cell. 
They are to be built up into body materials, and they or the 
body materials formed from them are to be torn down by 
oxidation that the energy resulting therefrom may be set free. 
This energy in its various forms is the manifestation of the life 
of the cell and the animal. 

Metabolism, Anabolism, Katabolism. — The two processes, 
viz. the one building up, the other tearing down, are most inti- 
mately connected. The building-up process, by which the 
body substance is formed from absorbed food material is known 

190 



METABOLISM 191 

as anabolism, and the tearing-down and oxidation process as 
katabolism. The double process is termed metabolism. 

Metabolism then means the double process by which the 
digested and absorbed animal food is first built up by anabolism 
and then torn down by katabolism, in which latter process energy 
is liberated, thus fulfilling the complete function of food. The 
entire double process includes all the changes which the original 
food material undergoes subsequent to digestion and absorption. 
These latter processes simply prepare the food and convey it 
to the animal cells where the metabolic changes take place. 

As will be readily understood, this process of metabolism is 
not simple, but becomes often very complicated both because of 
partial changes and because of transformations from one form 
of substance into another. Many of the intricate changes 
occurring in metabolism have not yet been made clear by 
means of physiological and physiological-chemical investiga- 
tions, but are still subjects of discussion and experimentation. 
It will not be profitable, therefore, in this study to enter into 
the discussion of many of these questions. We shall consider, 
therefore, only the fundamental facts and certain details which 
have been well established by experimental evidence. 

METABOLISM OF CARBOHYDRATES 

Direct Metabolism 

The metabolic changes which carbohydrate food undergoes 
in the animal body are more thoroughly understood than are 
those of either fats or proteins. We shall discuss these changes 
more fully than those of the other two food constituents, not 
because they are more important, but because they can be 
made clearer in an elementary treatment. 

As previously explained, the carbohydrate food which is 
eaten by an animal is changed by the combined digestive actions 
into the form of the three common hexose monosaccharoses, 
viz. glucose, fructose and galactose. In the normal diet of a 
mature animal, in which starch is the predominating carbo- 



192 ORGANIC AGRICULTURAL CHEMISTRY 

hydrate food, glucose is very much in excess of the other two 
digestive products. In the case of infants, galactose is also 
present in equal amounts with the glucose. By the process of 
absorption or assimilation, these three monosaccharoses are 
taken up by the blood capillaries of the small intestine and they 
are all found in that part of the blood circulatory system which 
leads to the portal vein. After a meal rich in carbohydrate food 
the amount of glucose, or of the three hexoses together, may be 
as much as 0.2 per cent, which is double the normal amount. 
The portal vein leads to the liver, and the three products of 
carbohydrate digestion are thus carried to this organ. 

Glycogen. — In the liver, due probably to enzymatic action, 
the first metabolic change occurs. This change is anabolic in 
character, and the result is the conversion of the three hexoses 
found in the portal vein into the polysaccharose glycogen. This 
glycogen is stored in the liver cells and in some cases may 
amount to as much as 10 per cent of the liver itself. 

The blood which is brought to the liver by the portal vein 
leaves the liver by the hepatic vein and passes thus into the 
general venous blood stream which reaches by means of fine 
capillaries the muscle cells of the whole body. It is a striking 
fact that while the glucose content of the portal vein varies in 
its amount with the supply of assimilated carbohydrate food 
the glucose content of the hepatic vein and general venous 
system remains constant at 0.1 per cent. 

Conversion of Glycogen into Glucose. — Furthermore, while 
the portal vein, which receives its supply of sugar from the 
absorbed food, may contain all three of the hexoses mentioned, 
the hepatic vein contains only glucose. This constant supply of 
glucose is maintained by the katabolic conversion of the liver glyco- 
gen into glucose. This change, also occurring in the liver, is like 
the preceding anabolic change of glucose, fructose and galactose 
to glycogen, without question brought about by enzymes. 

Amount of Glycogen in the Liver. — The amount of glycogen 
stored in the liver, like the amount of hexose sugars present in 
the blood of the portal vein, increases with the increase of ab- 



METABOLISM 1 93 

sorbed carbohydrate food. With an abundance of such food 
the amount of glycogen reaches its maximum of 10 per cent 
of the weight of the liver, in man. A gradual conversion of the 
liver glycogen into glucose is constantly going on in order to 
maintain the constant supply of 0.1 per cent of glucose in the 
general venous circulation. If the supply of carbohydrate food 
is diminished or cut off, this constant conversion of glycogen 
into glucose gradually exhausts the supply in the liver and it 
may fall to practically nothing. So far as is known, however, 
there is no passage of absorbed carbohydrate food into the 
general circulation except through the form of liver glycogen. 
The liver is thus not only a storehouse of carbohydrate food 
material, but is a kind of regulating reservoir by which a vary- 
ing supply of absorbed carbohydrate food is passed on to the 
general circulation in a constant supply of 0.1 per cent of the 
blood. Without going into detail, which would involve the 
discussion of yet unsettled questions, it may be stated that car- 
bohydrate food of a pentose nature derived from pentosans in 
vegetable foods probably passes through the form of liver gly- 
cogen and reaches the general circulation as glucose. 

Oxidation of Glucose. — What now is the fate of the constant 
supply of glucose furnished by the liver to the general circula- 
tion? The hepatic vein leads to venous capillaries which ter- 
minate in the muscle cells. In this way the glucose product of 
carbohydrate food reaches the ultimate cells of the animal and 
in these cells the oxidation takes place by which the energy of 
the carbohydrate food is liberated. By means of the arterial 
blood system leading from the lungs the muscle cells receive also 
a supply of oxygen in the form of oxyhemoglobin of the arterial 
blood. Within the cell the oxyhemoglobin gives up its oxygen 
to the glucose brought by the venous blood and oxidation of the 
glucose takes place in accordance with the reaction, 

C 6 Hi 2 6 + 6 2 -> 6 C0 2 + 6 H 2 + energy 

Oxidizing enzymes are probably the agents which produce this 
reaction. The reaction does not take place as simply as in- 
o 



194 ORGANIC AGRICULTURAL CHEMISTRY 

cheated, for lactic acid, which is a normal constituent of muscles, 
is probably an intermediate product. 

The rate at which this oxidation takes place is dependent 
upon the activity of the muscle cells. Certain muscular activi- 
ties, such as the involuntary actions of the body connected 
with the maintenance of body heat, body tone or tension, and 
the processes of circulation, respiration and digestion, are con- 
stantly going on and a large part of the energy of the food of 
animals is so expended. Another part of energy of animal food 
is used for producing muscular work which is voluntary, and 
varies with the physical or muscular activity of the animal. 
The total energy demands of the body regulate the demands 
upon the supply of glucose in the blood, and thus upon the 
reserve supply of glycogen in the liver. In general it may be 
said that under normal conditions of feeding and activity the 
supply of glycogen in the liver is used up between two succeed- 
ing meals. 

Muscle Glycogen. — The liver is not, however, the only place 
where carbohydrate food is stored in reserve in the form of 
glycogen. In case the maximum amount of glycogen has been 
stored in the liver and the supply of carbohydrate food is still 
in excess of the energy demands of the body, then the glucose 
of the general circulation on reaching the muscle cells is not all 
oxidized but, here likewise, is partly converted into glycogen 
and stored in the muscles as muscle glycogen. The amount 
possible of storage in this form may attain a maximum of 2.0 
per cent of the muscles which, though less in percentage amount 
than in the liver, may amount in total to much more, owing to 
the far greater mass of the muscle tissue over that of the liver. 
With an increase in the energy demands of the body or a de- 
crease in the food supply, this muscle glycogen is first drawn 
upon, being converted back into the form of glucose. In all of 
these metabolic changes enzymes play a most important part. 
Probably each metabolic reaction is brought about through 
their agency. 



METABOLISM 195 

Conversion of Carbohydrates into Fats 

The carbohydrate metabolism thus far discussed may be 
considered as the most direct metabolic change which carbo- 
hydrates undergo, in order to yield their energy to the animal 
body. In these changes the carbohydrate remains always as 
carbohydrate, simply passing from mono- to poly-saccharoses, 
and vice versa, until it is finally oxidized. Another metabolism 
of carbohydrates occurs, however, in which they become con- 
verted into compounds that are not carbohydrates. This is 
the metabolic conversion of carbohydrates into fats. 

The fact that the feeding of carbohydrate food increases the 
fat of animals has long been known and is the basis of practical 
animal feeding. The farmer feeds, not fat food, but largely 
carbohydrate food, e.g. grain, in order to increase body fat or 
to maintain a large production of milk fat. We cannot follow 
in detail the reactions by which carbohydrate food is converted 
into fat, but we can simply state the fact that such conversion 
does take place in the animal body. It is probably true that 
fat is not formed from carbohydrates until both liver glycogen 
and muscle glycogen have been stored to their maximum 
amounts ; that is, until all temporary reserve supplies for energy 
demands are filled. When such a condition occurs and the 
supply of carbohydrate food is still in excess, then this excess 
carbohydrate becomes converted into fat. 

Feeding Experiments. — While this conversion is a fact, as 
shown by common feeding practice, it has likewise been estab- 
lished by direct experiment. By feeding pigs and milch cows 
with rations carefully analyzed and calculated for the exact 
amounts of carbohydrate, fat and protein eaten and digested ; 
and then, similarly, accurately determining the gain in fat, in 
the case of the pigs, and the amount of milk fat produced in 
the case of the milch cows, it has been proven in both cases 
that the fat produced was very largely in excess of that possible 
of formation from the fat and protein of the food and must, 
therefore, have been formed from the carbohydrate. 



196 ORGANIC AGRICULTURAL CHEMISTRY 

Respiratory Quotient. — Another proof of the metabolic con- 
version of carbohydrates into fat is furnished by a study of 
what is termed the respiratory quotient. The two classes of 
compounds concerned, viz. carbohydrates and fats, are alike 
in containing the elements carbon, hydrogen and oxygen. 
They differ, however, in the relative proportions of these ele- 
ments. On oxidizing, the products of oxidation are alike in 
both cases, being simply carbon dioxide and water. As the 
relative amount of oxygen in each compound is different, the 
amount of added oxygen necessary for complete oxidation is 
different also. This will be made clear if we write the reactions 
for the oxidation of the two substances. Glucose, as we have 
just discussed, is the final form in which carbohydrate food is 
oxidized. Taking this as our example, we have the reaction of 
oxidation as follows : 

C 6 Hi20 6 + 6 2 -> 6 C0 2 +6 H 2 

1 mol. 6 mol. 6 mol. 6 mol. 

6 vol. 6 vol. 

This means that to oxidize one molecule of glucose 6 molecules 
of oxygen are required and 6 molecules of carbon dioxide are 
produced. Now, by a fundamental hypothesis of chemistry 
(Avogadro's Hypothesis) equal molecules of gases represent 
equal volumes. Therefore, in the oxidation of glucose the 
volume of oxygen gas used is exactly equal to the volume of 
carbon dioxide gas produced. 

If now we write the corresponding reaction for the oxidation 
of a fat, we have, taking glyceryl tri-stearate as an example : 

2 C57H110O6 + 163 O2— > 114 C0 2 +110 H2O 

163 mol. 114 mol. 
163 vol. 114 vol. 

This means that in the oxidation of fats, which contain less 
oxygen relatively than do carbohydrates, the volume of oxygen 
used is greater than that of the carbon dioxide produced. 



METABOLISM 197 

If we express these results in the form of a ratio between the 
carbon dioxide produced and the oxygen used, we have : 

Vol. CO2 r i i j , 6 vol. 1.0 

„ , ^ = for carbohydrates = — = 1.0 

Vol. 2 6 vol. 1.0 

r r . 114 VOL 0.7 

= for fats — a = — L = 0.7 

163 vol. 1.0 

Now in the animal body the oxidation of the food products or 
body substance is brought about in the muscle cell by the oxygen 
of the inhaled air and the carbon dioxide gas produced by the 
reaction is then exhaled by the lungs. The two gases then are 
involved in the process of respiration and this quotient, be- 
tween the carbon dioxide and oxygen, in the oxidation of car- 
bohydrates or fats, may be determined by accurately measur- 
ing the oxygen inhaled and used and comparing it with the 
carbon dioxide produced and exhaled. This quotient is there- 
fore known as the respiratory quotient. 

When now an animal that is fasting and in which all reserve 
carbohydrate food has been used up is examined, by a deter- 
mination of this quotient it is found that the quotient approxi- 
mates 0.7, the value for the oxidation of fats. This must mean 
that the animal is using up body fat as fuel for the energy pro- 
duction of the body. 

In a similar way if the animal body is supplied with a suffi- 
cient supply of carbohydrate food, but not an excess, the respi- 
ratory quotient approximates 1.0, the value for the oxidation of 
carbohydrates. This means that under these conditions the 
animal is using, as fuel for its energy production, only carbo- 
hydrate food. When the carbohydrate food supply is less than 
sufficient to furnish the necessary energy of the body, it is found 
that the respiratory quotient lies between 0.7 and 1.0, which 
means that the body is oxidizing both carbohydrates and fat. 

If, however, the animal is fed a large excess of carbohydrate 
food, so that both liver glycogen and muscle glycogen are stored 
to their maxima, it is found that a determination of the 
respiratory quotient gives a value greater than 1.0. This can 



198 ORGANIC AGRICULTURAL CHEMISTRY 

mean only one thing, that is, that, as the carbon dioxide ex- 
haled is greater in volume than the oxygen used, some oxygen 
must have been supplied from some other source than the 
inhaled air. If now we try to convert carbohydrates into fats, 
we find that in doing so some of the oxygen of the carbohydrate 
must be given off as free oxygen. 

19 C 6 Hi20 6 -> 2 CstHhoOg +4H2O + 49 2 
Glucose Glyceryl tri-stearate 

This free oxygen obtained from the conversion of carbohydrates 
into fats would then be used to oxidize other carbohydrate and 
thus diminish the oxygen required by inhalation, so that the 
ratio of carbon dioxide exhaled to oxygen inhaled would be 
greater than 1.0. 

Thus the experimental fact that with excess of carbohydrate 
food the respiratory quotient becomes greater than 1.0 can mean 
only one thing, viz. carbohydrate is being converted into fat. 

We have then not only results of feeding experiments but 
also results of the respiratory quotient proving that in the 
animal body carbohydrate food is metabolized into body fat 
or into milk fat. The body fat so formed is, in part at least, 
simply a more lasting reserve form of storing the excess of car- 
bohydrate food. On fasting, this body fat is drawn upon for 
producing energy as is shown by loss in body fat in fasting, or 
in the case of hibernating animals. 

METABOLISM OF FATS 

The digestive action upon the fat constituents of food results 
in the hydrolysis of the fats into fatty acids and glycerol. In 
this form the fat food is absorbed through the intestinal wall 
and enters the capillaries, not of the blood circulatory system, 
as do the products of carbohydrate digestion, but of the lym- 
phatic system, from which they pass to the portal vein and thence 
through the liver to the general venous system, where they are 
present in the blood plasma or liquid constituent of the blood. 
The fatty acids are rendered soluble and diffusible by means 



METABOLISM 199 

of the bile. In the lymph and later in the blood plasma, the 
products of fat digestion appear not as fatty acids and glycerol, 
but as recombined fat in a soluble form, giving to the blood 
plasma a turbid character, in case large amounts of fat have 
been eaten. In this form in the blood plasma, the absorbed 
and recombined hydrolytic products of fat food may become 
oxidized on reaching the muscle cells in a similar way to that 
by which the glucose is oxidized. In case the fat carried in the 
blood plasma is not required to be burned to furnish the energy 
supply of the body, the soluble fat in the blood plasma becomes 
reconverted again into the ordinary insoluble form and is 
deposited as fat globules which eventually form the fatty or 
adipose tissue of the body. 

Body Fat and Milk Fat. — The occurrence in body fat and 
also in milk fat of certain characteristic fats eaten as food has 
led to the belief held by some that fat food is absorbed in the 
form of an emulsion of unhydrolyzed fat. The fat of hogs which 
have been fed on cottonseed meal has been shown to give the 
tests for cottonseed oil. Also the milk fat of cows which have 
been fed on sesame oil cake responds to the tests for sesame oil. 
It is generally accepted, however, that the presence of such 
fats in the body and milk is not incompatible with the idea 
that all fat food is hydrolyzed into fatty acids and glycerol. 
The reversible nature of the enzymatic reaction, especially of 
lipolytic enzymes, is well established ; and this reversible reaction 
may take place even during the passage of the hydrolytic 
products through the wall of the digestive tract, so that, when 
the assimilated products of digested fat food first appear in the 
lymphatic capillaries, they are in the form of recombined fat, 
and not of the separate hydrolytic products. This recom- 
bined fat synthesized from the hydrolytic products so imme- 
diately would thus appear in the lymph and blood plasma and 
then in the muscle cells or in the milk in the same form in 
which it was eaten. 

When the absorbed products of fat food are thus metabolized 
into the fat of blood plasma, and this fat is not used as fuel to 



200 ORGANIC AGRICULTURAL CHEMISTRY 

supply energy, it is deposited as body fat. This body fat may 
later be drawn upon to supply energy, in which case it is recon- 
verted into the soluble form and again enters the blood of the 
muscle cells and is oxidized. This is proved by experiment 
upon fasting or hibernating animals in which body fat is lost 
in proportion to the energy set free. 

Conversion of Fats into Carbohydrates. — There is still a 
question as to whether body fat, or even the first formed fat in 
blood plasma, is burned directly as fat or is first converted into 
glucose. Experimental evidence seems to indicate, however, 
that while body fat may be first converted into glucose and 
then oxidized, yet directly absorbed food fat is undoubtedly 
burned in the body, that is, in the muscle cells, without being 
first converted into glucose. Such a conversion of food fat into 
glucose preceding oxidation would result in the loss of a con- 
siderable proportion of the fuel value of the fat, whereas experi- 
ments have shown that almost the full amount of the fuel value 
of fat food is utilized as energy in the animal body. 

We have, nevertheless, almost as conclusive evidence that 
body fat is at least possible of conversion into glucose. In 
fasting or hibernating animals the blood maintains its constant 
amount of glucose, viz. o.i per cent. This constant supply of 
glucose in the blood could only be maintained under these con- 
ditions by the conversion of body fat into glucose. Also in 
these cases the respiratory quotient has been found to be below 
0.7, the value of the quotient when fat alone is oxidized. Such 
a value for the respiratory quotient must mean that fat is being 
converted into glucose, just as the value greater than 1.0 means 
that carbohydrate is converted into fat, as previously dis- 
cussed. It has also been shown that the glycogen content of 
the body has increased, in the case of hibernating animals, at 
the expense of body fat. This conversion of fats into carbo- 
hydrates is thought to take place in the liver, and as this organ 
contains a very large number of different enzymes such a trans- 
formation is not improbable. It is possible that the formation 
of carbohydrate from fat takes place only from the glycerol 



METABOLISM 201 

part of the molecule, as such a conversion of glycerol into glu- 
cose would be much simpler than of the entire fat molecule. 
This view is not, however, in accord with the results indicating 
the transformation of fat into carbohydrate by the production 
of a respiratory quotient below 0.7. Taken all together, there- 
fore, while the evidence of the conversion of fat into carbo- 
hydrate is not as conclusive as that indicating the reverse for- 
mation of fat from carbohydrate, it is, nevertheless, pretty well 
established, at least so far as body fat is concerned. 

While the greater part of the fat of the body and of milk is 
formed from carbohydrate food, yet food fat itself also yields 
body fat. The proportion of the food fat that is utilized 
directly for the production of energy varies with the diet and 
with the energy requirements of the animal body. Probably 
in most cases, except when body fat is increasing or milk fat 
is continually produced, the greater part of the fat food is 
almost directly converted into heat energy, for, as we shall 
find, fat is the highest energy food constituent of the three. 

METABOLISM OF PROTEINS 

The metabolism of the protein food is much more compli- 
cated than that of either of the other constituents and there are 
many points not yet made clear and concerning which there is 
more or less discussion and difference of opinion. We shall 
therefore not pretend to take up the subject in its entirety or 
to consider any point of it in very great detail. 

The difference between proteins and carbohydrates or fats, 
as has been repeatedly stated, is that they only, of the three 
organic food constituents, contain the element nitrogen. The 
complicated reactions connected with the metabolic changes of 
this element nitrogen present exceedingly difficult problems which 
have not yet been fully explained and proved by investigation. 

Amino-acids. — The results of the combined processes of 
digestion upon protein food constituents is their cleavage into 
the ultimate products of protein hydrolysis, viz. the amino- 



202 ORGANIC AGRICULTURAL CHEMISTRY 

acids. It was formerly believed that all absorption of digested 
protein was in the form of amino-acids. The presence of the 
enzyme erepsin in the intestinal juice seemed to uphold this 
view for, as this enzyme completes all partially digested protein, 
carrying the hydrolysis through to the amino-acids, its presence 
would indicate that the complete hydrolysis is necessary for 
absorption. It is now pretty generally accepted, however, 
that all protein food is not converted into amino-acids. The 
experimental evidence for this is that amino-acids themselves, 
at least singly, are not used as nutritive material when fed to 
animals. It seems possible, however, that certain combinations 
of amino-acids, including some of the more complex ones like 
tryptophane, can be utilized directly as food. 

Polypeptide Nucleus. — On the other hand, it has been found 
that tryptic digestion is inactive toward certain polypeptides, 
and it is believed that this indicates a sparing or protective 
action toward the further hydrolysis of these compounds in 
order that they may be absorbed as such. Being absorbed 
through the intestinal wall together with the amino-acids, these 
polypeptides act as a nucleus with which the amino-acids com- 
bine to form new protein. It has been established that neither 
polypeptides nor amino-acids are present in the blood except 
perhaps small amounts of the latter. This would indicate that, 
as in the case of fats, the resynthesis of the protein from the 
polypeptide and amino-acid products of digestion occurs during 
the absorption of these materials through the intestinal wall. 

Serum Albumin. — As stated, the absorbed products of pro- 
tein digestion are found in the blood capillaries leading to the 
portal vein. In the blood of this part of the circulatory system 
there is always present in the serum a protein known as 
serum albumin. It is interesting that while absorbed and 
resynthesized fat is found in the animal body of exactly the 
same nature as the food fat, even though this is different in 
character from the normal body fat, yet, in the case of pro- 
teins, no matter how different the protein food may be from 
the serum albumin of the animal, the serum albumin synthe- 



METABOLISM 203 

sized from the food protein is always the same. The selective 
action of the digestive enzymes in not hydrolyzing certain poly- 
peptides would be in accord with such results. The animal 
body in its digestive action upon proteins would retain certain 
polypeptides in an unhydrolyzed form, while all others would 
be completely hydrolyzed to amino-acids. These unhydrolyzed 
polypeptides would then act as a nucleus with which the various 
amino-acids could combine to synthesize a protein of uniform 
character, viz. the serum albumin. 

Body Protein. — What now is the fate of the synthesized 
serum albumin of the blood? We know that the blood protein 
synthesized from the absorbed products of food protein is built 
up in the muscle cells into body protein, but we do not know the 
different steps in this metabolic change. It is important here 
to emphasize the fact that under normal conditions body pro- 
tein can be formed, either directly or indirectly, only from food 
protein. Unlike plants, animals are unable to use other nitrogen 
compounds together with carbohydrates to synthesize body pro- 
tein. It is true that for a short time the animal body can live 
with a protein free diet, but this is always at the expense of 
body protein, and any formation of body protein from carbohy- 
drates can only take place when protein residues, probably 
polypeptides and amino-acids obtained from the katabolism of 
body protein, are present to combine with carbohydrate to form 
new body protein. Under such conditions body protein is 
gradually lost and protein katabolism grows gradually less and 
less until life ceases. Food proteins in some form, or com- 
pounds analogous to them, such as certain combinations of 
amino-acids or polypeptides or both, and these only under 
limited conditions, are absolutely essential to the formation of 
body protein and the existence of animal life. 

Oxidation of Protein. — We do not know certainly whether 
all food protein first converted into blood protein is built up 
into body protein and then this body protein torn down and 
oxidized, or whether only part of it forms body protein while 
another part is oxidized without ever having been converted 



204 ORGANIC AGRICULTURAL CHEMISTRY 

into body protein. It seems probable that part of the protein 
is oxidized immediately and never forms body protein. This 
may take place with the entire blood protein molecule, or it is 
possible that in being synthesized into the various forms of 
body protein certain groups of the blood protein are unadapted 
for the synthesis of the body protein and these portions then 
become oxidized. 

While we cannot therefore follow with any definiteness the 
conversion of food protein into body protein or state definitely 
whether katabolized protein is body protein or blood protein 
(food protein), we can follow in certain detail the results of the 
katabolism of protein in the body. 

Katabolism of Proteins. — We have thus far discussed, 
though without a much to be desired definiteness in detail, the 
conversion of food protein into body protein. It remains to 
consider the reactions and results of the katabolism or degrada- 
tion of protein and the oxidation by which it, like carbohydrates 
and fat, yields energy to the animal body. For a long time it 
was held that protein alone was the material of the body from 
which muscular energy was derived. This is not now considered 
as true, for it has been shown that both carbohydrates and fats 
contribute to the supply of muscular energy. 

Katabolic Products. — In considering the katabolic or tear- 
ing down changes of protein it is necessary to remember that 
proteins, because of their containing nitrogen as well as carbon, 
hydrogen and oxygen, may be looked upon as consisting of two 
parts, viz. (i) a carbon, hydrogen and oxygen part, which acts 
like the carbohydrates and fats and on oxidation yields carbon 
dioxide and water as the products, (2) a nitrogen-containing 
part, also containing carbon, hydrogen and oxygen, which on 
oxidation yields distinctly different products. It is not meant 
that in the protein molecule there are two separate portions united 
together, but simply that by their oxidation two classes of prod- 
ucts are formed. It is through a study of these end products of 
protein katabolism that we gain an insight into the process itself. 

When protein is oxidized in an excess of oxygen, as in a calo- 



METABOLISM 205 

rimeter, the products are carbon dioxide, water and nitrogen; 
and the theoretical fuel value or calorific value of proteins 
is in accordance with such a reaction. In the animal body, 
however, the reaction does not take place in just this way. 
The products formed here are carbon dioxide, water and complex 
nitrogen compounds such as urea, uric acid and the purine 
bases. The carbon dioxide and water are eliminated in the 
respiration as in the case of carbohydrates and fat. 

Nitrogen Excretion in Urine. — The nitrogen-containing 
compounds are all eliminated through the kindeys in the urine. 
It is important to emphasize the fact that the urine is thus a 
true excretion substance, carrying out from the body the end 
products of metabolism, exactly analogous to the exhaled 
breath and not like the feces, which are almost entirely a waste 
product of undigested food material. The urine contains all 
of the nitrogen of the katabolized protein and about go per cent 
of this nitrogen is in the form of urea, only the other 10 per cent 
being in the form of uric acid arid the other nitrogen compounds 
of urine. Thus a study of the urine nitrogen is the means we 
have of studying the nitrogen portion of katabolized protein. 
Also the total nitrogen of the urine is a measure of the total katab- 
olism of protein and approximately every 16 grams of urine nitro- 
gen represents 100 grams of protein that have been katabolized. 
This explains the importance of nitrogen analysis of urine. 

Formation of Urea, etc. — Let us now examine in more detail 
the way in which the protein nitrogen is converted into urea. 
When protein is oxidized under the conditions present in the 
muscle cells, or perhaps by a preceding hydrolysis of the protein 
molecule, the nitrogen splits off in the form of ammonia. This 
is readily understood when we remember that proteins are poly- 
peptide compounds of amino-acids. Illustrating by a simple 
amino-acid the hydrolysis occurring we have : 

H 2 Ni-CH 2 -COOH 

j + -> NHs + CH2OH -COOH 

Hi- OH 



206 ORGANIC AGRICULTURAL CHEMISTRY 

By the further oxidation of these products we would obtain 
carbon dioxide and water from the carbon-hydrogen-oxygen 
portion, the ammonia remaining as ammonia. From our study 
of the chemistry of urea in Section I (p. 97) we know that urea 
may be synthesized from ammonia and carbon dioxide. Thus 
part of the carbon dioxide of the complete oxidation would 
remain combined with the ammonia as urea. This explains what 
we shall later consider again, that the theoretical calorific value 
or energy value of protein is not obtained in the animal body, 
because a part of this energy is lost in urea and the other nitro- 
gen compounds of urine. In practice, therefore, we subtract 
from the theoretical calorific value of protein the calorific value 
of the urine to obtain the physiological or body calorific value 
of protein. 

This would seem to indicate that in the katabolism of protein 
a hydrolytic cleavage of the molecule into a nitrogenous un- 
oxidizable portion and a non-nitrogenous oxidizable portion 
must precede the oxidation, for if the oxidation occurred with 
the protein molecule before splitting, we should expect all of 
the carbon and hydrogen to be oxidized, and the body calorific 
value of proteins would be more nearly equal to the value ob- 
tained in a combustion calorimeter. 



Conversion of Proteins into Carbohydrates 

What now happens to this non-nitrogenous portion of the 
protein molecule? We know that such a portion would be 
capable of immediate oxidation and we know also that even- 
tually it is completely oxidized, though not all of its energy of 
oxidation is liberated, some of the carbon dioxide combining 
with the ammonia, the other hydrolytic product of the protein, 
yielding urea. Whether the oxidation of the non-nitrogenous 
portion takes place immediately or whether other metabolic 
changes occur before oxidation is not clear. 

It has been claimed that all of the oxidation in the body by 
which energy is liberated is the oxidation of glucose and that 



METABOLISM 207 

all food materials are finally converted into this sugar before 
they are oxidized to yield energy. This has not borne the 
test of experiment in the case of fats, though we know that in 
the body fats may be converted into carbohydrates. With 
the proteins also we are not able to claim that such a trans- 
formation of the products of protein cleavage into carbohydrates, 
before oxidation, always takes place, though we can show that 
such a conversion is possible. 

In the cleavage of proteins alanine or a-amino-propionic acid 
is one of the normal products, and this by hydrolysis, as already 
mentioned on page 85, would yield ammonia and lactic acid 
(a-hydroxy-propionic acid). We know that lactic acid is 
formed in the body from glucose, such a conversion being simply 
a splitting of the molecule without hydrolysis. 

CeHuOe-*^ C 3 H 6 3 , (CHa-CH(OH) -COOH) 

Glucose Lactic acid 

It would not, therefore, be impossible for the reverse action 
to occur and glucose to be formed from the lactic acid resulting 
from the non-nitrogenous portion of protein. That a formation 
of carbohydrates from protein actually does take place in the 
animal body has been proved by experiment. It has not been 
proved, however, that all non-nitrogenous protein cleavage prod- 
ucts are first converted into carbohydrates before oxidation. 

The actual conversion of proteins into carbohydrates does 
take place in the body in case there is a lack of carbohydrate 
and fat food. In such cases the normal supply of glucose in the 
blood is maintained wholly by protein, and also the glycogen 
supply in the liver may be similarly kept up. 

Conversion of Proteins into Fats 

That both body fats and milk fats may be formed from pro- 
teins has been well established by experiment. Whether such 
a conversion is direct from proteins to fats, or indirect from 
proteins through carbohydrates to fats, is not so well proved. 



208 ORGANIC AGRICULTURAL CHEMISTRY 

We have just demonstrated that proteins can be converted into 
carbohydrates, and the conversion of carbohydrates into fats is 
likewise proved. 

Thus protein food may yield both carbohydrates and fats 
from the non-nitrogenous portion of the molecule, and this por- 
tion, whether it is thus transformed or not, is eventually oxidized 
with the liberation of energy. This energy, however, is not 
equal to the entire energy of the original protein molecule, as a 
portion of it remains locked up, with the nitrogen portion of the 
protein, in the form of urea and other nitrogen excretion products 
of protein katabolism. 



CHAPTER XIII 

MILK, BLOOD AND URINE 

Before dismissing the general subject of animal food and 
nutrition, and taking up the study of plant physiology, it is 
best to consider the three animal fluids mentioned at the head 
of this chapter. Milk is a normal secretion of all mammalian 
animals, serving as food for the offspring during the first period 
of its life. Blood is the main circulatory liquid of the animal 
body by means of which the absorbed food nutrients are carried 
to the different parts of the body and in the muscle cells brought 
in contact with oxygen, also carried by the blood, and finally 
oxidized. Urine is an excretion liquid which serves as the 
medium by which the nitrogen end products of protein katab- 
olism are removed from the body. 

MILK 

Milk is the normal secretion of the mammary glands of 
mammalian animals. It is provided by the animal as the sole 
food of the young for the first period of its life. In harmony 
with this use it is natural to find that it contains all of the 
substances essential as animal food. These substances, as we 
have previously stated, embrace carbohydrates, fats, proteins 
and certain inorganic salts. As an agricultural product milk 
means almost exclusively cows' milk and, unless otherwise 
stated, what we shall say refers to this particular milk, though 
in general the statements will apply also to all milk. 

Constituents 

Carbohydrates. — There is only one carbohydrate found in 
milk, viz. milk sugar, or lactose. This sugar is a disaccharose 
of the same composition as cane sugar, i.e. C12H22O11. It is 
p 209 



210 ORGANIC AGRICULTURAL CHEMISTRY 

easily soluble in water and crystallizes in large crystals. It 
does not taste quite as sweet as cane sugar, but is more easily 
digested ; at least human beings, and probably all mammals, 
are able to digest it before any other carbohydrate. It is the 
sole carbohydrate food so long as the animal lives upon milk 
alone. It reduces Fehling's solution and may be tested for or 
determined quantitatively by means of this reagent. 

An important property of milk sugar is that certain bacteria, 
viz. lactic acid bacteria, ferment it with the production of lac- 
tic acid. The lactic acid so produced is the cause of what is 
termed the souring of milk and is also connected with the sepa- 
ration of the protein casein. Milk sugar is obtained from milk 
in considerable quantities for use as an infant food and the 
sugar left in whey is used without separation for the commer- 
cial preparation of lactic acid. 

Fats. — The fat constituents of milk are contained largely 
in the cream, which may be separated from it, and in butter 
the most important milk product. As has been previously ex- 
plained, fats are esters of glycerol and organic acids. With 
two exceptions, the acids present as esters in milk fat belong 
to the monobasic saturated acids of the acetic acid series. The 
exceptions are oleic acid, the eighteen-carbon acid of the ethy- 
lene unsaturated series, and a dihydroxy derivative of stearic 
acid, the eighteen-carbon saturated acid. 

The acids found in milk fat, as glycerol esters, are the follow- 
ing in the order of their amounts present as given by Browne : 

Palmitic acid G5H31COOH 

Oleic acid G7H33COOH 

Myristic acid Ci 3 H 27 COOH 

Butyric acid C 3 H 7 COOH 

Laurie acid C11H23COOH 

Caproic acid C5H11COOH 

Stearic acid CnH^COOH 

Dioxystearic acid Ci 7 H 33 (OH) 2 COOH 

Caprylic acid C 7 H 15 COOH 

Capric acid C 9 H 19 COOH 



MILK, BLOOD AND URINE 211 

The fat of milk is held in suspension in the form of an emul- 
sion, and is one of the constituents to which the characteristic 
opaque white color is due. Owing to the fact that its specific 
gravity is less than that of water it rises to the surface on 
standing in the form of cream, or it may be separated by sub- 
jecting the milk to a strong centrifugal action as in the ordinary 
milk separator. The size of the fat globules present in the 
emulsion varies with the particular breed of cow and with the 
period at which the milk is obtained. Barthel gives the size 
as o.oooi to 0.022 mm. in diameter with an average of 
0.003 mm - 

The particular physical and chemical properties of milk fat 
which serve as a basis of analysis will be referred to under 
butter. The simple determination of the amount of fat present 
in milk is carried out in the laboratory by absorbing the milk 
into a porous block of filter paper and then subjecting this, after 
drying, to extraction with ether or light petroleum oils (benzine) . 
After evaporation of the solvent the fat is left practically pure. 
In the dairy the determination is made by means of the well- 
known Babcock method. The principle upon which this 
method is based is that, by the addition of a certain amount of 
sulphuric acid, the specific gravity of the milk liquid is raised 
considerably so that the fat separates very completely from its 
emulsion state. The separation is assisted by whirling the 
mixture in a centrifugal machine after first placing it in a specially 
constructed bottle with a narrow graduated neck. After cen- 
trifuging, the fat stands completely separated as a clear layer 
in the graduated neck and is read directly in per cent of fat in 
the milk. 

Proteins. — The protein constituents of milk are three, viz. 
caseinogen, a phosphoprotein ; an albumin, lactalbumin; and a 
globulin, lacto globulin. Caseinogen is in much greater amount 
than either of the other two, 85 per cent of the total protein 
being in this form. The lactalbumin constitutes most of the 
remaining 15 per cent, while the lactoglobulin is present only in 
traces. 



212 ORGANIC AGRICULTURAL CHEMISTRY 

Caseinogen is not soluble but is held in colloidal suspension, 
and it is this colloidal suspended protein together with the 
emulsified fat already mentioned which give milk its white 
opaque color. 

Casein or Curd. — When milk sours, due to the lactic acid 
fermentation of the milk sugar, or when sweet milk is acidified 
carefully with dilute acetic acid, the caseinogen is converted 
into wholly insoluble casein. The casein separates as a floccu- 
lent mass, or curd, which is the basis for the manufacture of 
cheese. 

This conversion of colloidal caseinogen into insoluble casein 
is also effected by a milk-coagulating enzyme or enzymes known 
as rennin. In the animal body gastric rennin in the gastric 
juice and pancreatic rennin in the pancreatic juice produce this 
change. Commercially, the enzymes obtained from animals 
are used under the name of rennet. 

The exact nature of the chemical changes that occur in this 
coagulation is not fully established, nor is it determined whether 
the enzyme coagulation is exactly the same as that produced by 
acids. The generally accepted view is as follows : The enzyme 
splits the caseinogen into a truly soluble form of protein and 
perhaps also yields a peptone. The soluble protein then unites 
with calcium, from calcium salts present in the milk, yielding a 
calcium salt of the protein which is the casein or curd. 

Lactalbumin. — After the separation of the casein from milk 
the filtrate is known as whey. This contains in solution the 
other two proteins lactalbumin and lacto globulin. On heating 
the whey the albumin coagulates just as egg albumin does, 
and may then be filtered off. The lactoglobulin does not coagu- 
late with heat and remains in the final filtrate. Its amount, 
however, is very small and we need not consider it further. 
The albumin obtained as above agrees in properties with other 
albumins, e.g. egg albumin and blood serum albumin, giving the 
characteristic protein reactions. 

Inorganic Constituents, Salts. — The salt constituents con- 
sist almost entirely of salts of inorganic acids. Only one organic 



MILK, BLOOD AND URINE 



213 



acid is present, viz. citric acid, which amounts to about 0.2 
per cent. The principal salts are chlorides and phosphates of 
the metals, sodium, potassium, calcium, magnesium and iron. 
Barthel gives the following for the composition of milk ash 
according to Fleischmann : l 

K2O 2 S-7 I P er cen t 

NazO 11.92 per cent 

CaO 24.68 per cent 

MgO 3.12 per cent 

Fe 2 3 0.31 per cent 

P2O5 21.57 per cent 

CI 16.38 per cent 

Also according to Soldner, 2 the same author gives the follow- 
ing as the salts present in milk. 



Sodium chloride . . . 
Potassium chloride . . 
Monopotassium phosphate 
Dipotassium phosphate 
Potassium citrate . . 
Dimagnesium phosphate 
Magnesium citrate . . 
Dicalcium phosphate . . 
Tricalcium phosphate . 
Calcium citrate . . . 
Calcium oxide (in casein) 



10.62 
9.16 

12.77 
9.22 
547 
3.7i 
4.05 
7.42 
8.90 

23-55 
5-i3 



per cent 
per cent 
per cent 
per cent 
per cent 
per cent 
per cent 
per cent 
per cent 
per cent 
per cent 



The salts of milk are in solution, and on evaporation of the milk 
to dryness and burning the dry residue they remain as an ash. 
The amount of ash is about 0.7 per cent. The total solids of 
milk, which include not only salts but also the organic con- 
stituents, amount to about 13.0 per cent, leaving about 87.0 
per cent of water. 

1 Fleischmann, "Lehrbuch der Milchwirtschaft," p. 56 (1907). 

2 Soldner, Landw. Vers-Stat, 1888, p. 370. 



214 ORGANIC AGRICULTURAL CHEMISTRY 

General Properties 

Milk has an opaque white color with a more or less yellow 
tint depending upon the amount of fat present. The opaque 
appearance, as previously stated, is due to the combined effect 
of the emulsified fat and the colloidal caseinogen. The physical 
properties and percentage composition of milk are fairly constant 
so that it is possible to establish standards of quality. Accord- 
ing to the U. S. Department of Agriculture, standard milk has 
the following composition in fat and total solids : 

Standard Milk 

Fat, not less than 3.25 per cent 

Total solids (not fat), not less than 8.5 per cent 

An average milk may be given as follows : 

Specific gravity 1. 029-1 .034 

Fats 4.0 per cent 

Proteins 3.3 per cent 

Milk sugar 5.0 per cent 

Ash 0.7 per cent 

Total solids 13.0 per cent 

A fat rich milk will contain approximately : 

Fats 5-39-7-76 per cent 

Proteins 3.66-4.68 per cent 

Milk sugar . . » 4.76-4.82 per cent 

Ash 0.75-0.83 per cent 

Total solids 14.62-18.03 per cent 

Extreme variations in composition may be : 

Fats 1. 04-14. 67 per cent 

Proteins 2.86- 9.98 per cent 

Milk sugar 2.33- 5.28 per cent 

Ash 0.66- 1.44 per cent 

Of the three organic constituents the fat varies most and the 
sugar least. 



MILK, BLOOD AND URINE 215 

Analysis of American milk by the Vermont Experiment 
Station in 1890 gave the following results: 

Total solids, p. c. . 11.35 n-77 12.21 12.75 I3-I7 I3-7I 14.25 U-77 15-17 15.83 

Fat, p. c 3-20 3.36 3.60 3.82 4.09 4.46 4.87 5.20 5.47 5.88 

Protein, p. c . . . 2.99 3.03 3.10 3.29 3.40 3.48 3.65 3.87 4.07 4.26 

Sugar and ash, p. c. . 516 5-38 5-5* 5-64 5-68 5.77 5-73 5-7© 5-63 5-69 



Analysis 

The determination of the specific gravity and the composi- 
tion of milk is usually carried out by different methods in the 
chemical laboratory and in the dairy or creamery. The specific 
gravity is the weight of a volume of milk compared with the 
weight of an equal volume of water both at the same tempera- 
ture or at definitely stated temperatures for each. In the 
laboratory this is determined by direct weighing. In the dairy, 
and also in the laboratory, it is usually made by the use of an 
hydrometer spindle graduated especially for use with milk. 
Such a hydrometer is called a lactometer. It may also be deter- 
mined by means of a Westphal balance. 

The total solids in milk are determined by evaporation and 
then weighing the dry residue. As the specific gravity varies 
with the total solids it is possible to calculate the latter from 
the former if the fat content is also known. A formula that 
has been worked out for use with direct Quevenne lactometer 
readings is as follows : 

Total solids = lactometer reading + (m x fet per ^ 
4 

The ash is determined by incinerating the dry residue or 
total solids at a low red heat and weighing the remaining ash. 
The proteins are determined by means of the Kjeldahl method 
for nitrogen as given under proteins (p. 93). A creamery 
method by means of the centrifuge has also been devised by 
Hart for determining milk casein. Fats are determined by 
extraction or by the Babcock method, as stated under milk 
fats. The determination of milk sugar may be made in the 



2l6 ORGANIC AGRICULTURAL CHEMISTRY 

whey by means of Fehling's solution. It is often, however, 
calculated from the total solids by subtracting fats, proteins 
and ash. 

Preservatives 

The preservatives used with milk include formaldehyde 
(formalin), hydrogen peroxide, boric acid and sodium carbonate. 
The testing and determination of these belong to the special 
field of food analysis and will not be discussed in detail. By 
means of the hydrochloric acid test formaldehyde may be de- 
tected in i part to 250,000. Hydrogen peroxide by the para 
phenylene diamine test may be detected in 1 part to 40,000. 
Boric acid by the turmeric paper test may be detected in 1 part 
to 8000, and sodium carbonate by hydrochloric acid on the ash 
may be detected in 1 part to 2000. Methods of procedure for 
these tests may be found in books on food analysis such as 
Leach, Sherman and Hawk. 

Butter 

The questions concerning the two important milk products, 
butter and cheese, belong more to a special study of dairy chemis- 
try or food analysis than to a general discussion of agricultural 
chemistry. In addition, therefore, to what has already been 
said in regard to the particular milk constituents characterizing 
these products, only a few facts will be given in regard to their 
general composition. 

Butter consists principally of the milk fat with a part of the 
other constituents of milk that are separated with the fat. 
The separated fat is subjected to churning and working opera- 
tions by which the fat is pressed together and mostly freed 
from the liquid known as buttermilk, when it takes on the 
appearance of ordinary butter, salt being added as flavoring 
and as a preservative. The average composition of butter 
may be given as follows, according to McKay and Larsen 
(Iowa) : 



MILK, BLOOD AND URINE 217 

Composition of Butter 

Fat 84.0 per cent 

Water 12.73 per cent 

Protein 1.30 per cent 

Ash and Salt 1.97 per cent 

The different substitutes for butter are of two types. Reno- 
vated or Process Butter consists of old rancid butter worked over 
to remove objectionable substances and to incorporate a small 
amount of fresh milk or cream. Oleomargarine, Butterine and 
similar products consist of mixtures of animal fats, other than 
milk fat, such as beef fat and lard, to which also some fresh 
milk or cream is usually added. 

Cheese 

Cheese consists principally of the coagulated casein of milk 
separated by natural souring of the milk or by the use of com- 
mercial enzyme preparations known as rennet (rennin). The 
curd carries down with it most of the fat and some of the other 
constituents of the milk. After separation the curd is worked 
into various forms of cheese, and most varieties, except the 
soft fresh cream cheeses, are subjected to a fermentation or 
ripening. The fermentation produces various substances 
which give to the cheese a particular character and flavor. 
The average composition of Cheddar cheese made in New York 
State may be given as follows, according to Van Slyke : 

Composition of New York Cheddar Cheese 

Water 32.7-43.9 per cent 

Fats ........ 30.0-36.8 per cent 

Proteins 20.8-26.1 per cent 

(Milk sugar, lactic acid, ash and salt about 5.0 per cent.) 

Whey. — The filtrate obtained when the coagulated casein 
is separated is known as whey. It contains the soluble pro- 
teins, practically all of the milk sugar, and some of the inorganic 



2l8 ORGANIC AGRICULTURAL CHEMISTRY 

constituents. It has food value for domestic animals, being 
used especially for swine. Commercially the whey is used as a 
source of milk sugar and, after fermentation, of lactic acid. 

Food Value 

The definite consideration of food values will be given in 
another chapter. As stated at the beginning of our study of 
milk it is a normal balanced food in itself, containing all of the 
essential food constituents. While primarily a normal food for 
young animals, including babies, it is also used to a very large 
extent as a food for adult human beings. The food value of 
butter is largely in its fat content and of cheese in both fat and 
protein. 

EXPERIMENT STUDY XXIX 
Separation of Milk Constituents 

(i) Casein. Dilute a pint of whole milk with an equal volume of 
water. Add slowly with slight stirring a dilute (10 per cent) solution 
of acetic acid. When flocculation begins, proceed very slowly and 
stop the addition of acid as soon as the coagulum becomes nearly 
solid. Allow to stand a few minutes until the coagulated protein 
separates slightly, leaving a whey that is only slightly opaque. Filter 
through a double cheesecloth and press the curd as dry as possible. 
This curd is casein with included fat. After extracting the fat as in 
(2) the casein should be white and quite easily pulverized. Test the 
dry casein by the tests for protein (Experiment XVIII, 4). 

(2) Fat. Place the pressed casein in a flask or bottle and cover 
with 95 per cent alcohol. Shake a little to aid the extraction of the 
water. Pour off the alcohol extract. Repeat the extraction with 
ether instead of alcohol and collect the ether extract by itself. Extract 
again and a third time if necessary with ether, combining the ether 
extracts. Distill off the ether from the extracts and a residue of milk 
fat will be obtained. 

(3) Lactalbumin. If the whey from the separated casein in (1) re- 
quires it, filter through a filter paper. Place the clear whey in an 
evaporating dish or beaker and heat to boiling for a few minutes. 
Notice the coagulation of the milk albumin. Filter off the albumin 
through filter paper and repeat the heating. If more albumin sepa- 



MILK, BLOOD AND URINE 219 

rates, filter again. Dry the albumin and make the protein tests. 
Test 10 c.c. of the filtrate from the albumin by the Biuret Test 
(Experiment XVIII, 4, c) to prove the presence of a non-coagulable 
protein (lactoglobulin). 

(4) Phosphates. Without separating the traces of lactoglobulin 
boil the albumin nitrate in an evaporating dish carefully until bump- 
ing occurs. Filter through paper. The separated solid is largely 
calcium phosphate, Ca 3 (P0 4 )2. Repeat the boiling with the filtrate 
from the calcium phosphate and obtain a second crystallization of 
phosphate. Repeat as many times as necessary until no more phos- 
phate separates. Test the collected phosphate by dissolving in dilute 
nitric acid and adding an equal volume of ammonium molybdate 
solution. A yellow precipitate proves the presence of phosphates. 

(5) Milk Sugar. When no more separation of calcium phosphate 
occurs, continue to evaporate the filtrate with a low flame so as to 
prevent charring. When quite small in volume (about 100 c.c.) 
transfer to a steam bath and continue the evaporation until the liquid 
is of a sirupy consistency. Cool, and see if any crystals separate. 
If not, evaporate further until crystallization does take place. Filter 
or decant off the liquid, wash the crystals with a little water, dry them 
on filter paper and examine by taste, etc. They are milk sugar 
(lactose). Dissolve a few crystals in water and test with Fehling's 
solution (Experiment XXII, 2). 

THE BLOOD 

While the blood is the chief circulatory fluid of the animal 
body, there is associated with it another known as lymph. In 
discussing the metabolism of food we have stated that the ab- 
sorbed food nutrients are carried to the cells by means of the 
blood, where they come into intimate contact with the oxygen 
brought from the lungs by means of the blood also. In bring- 
ing about this contact between oxygen and food nutrients 
within the cell, and thus effecting their final katabolism, the 
lymph plays a very important part and also in removing from 
the cells the waste products of katabolism. We shall not 
attempt to discuss in detail the exact part which each of these 
fluids takes in this utilization of food but present the general 



220 ORGANIC AGRICULTURAL CHEMISTRY 

facts in regard to the nature and properties of the more promi- 
nent of the two, viz. the blood. 

Properties. — The blood of mature animals is an opaque, 
dark red fluid with a neutral reaction according to the concen- 
tration of hydrogen and hydroxyl ions, but an alkaline reaction 
as ordinarily tested with litmus paper, due to the presence of 
sodium carbonate and phosphate. In man it has a specific 
gravity of 1.06 and the amount in the body equals about 7.5 
per cent of the body weight. 

Constituents 

The constituents of the blood are of two kinds, viz. organic 
and inorganic. These are present in two conditions, viz. either 
in true solution or in suspension in the liquid substratum, water. 
The liquid portion of the blood, including both the solvent and 
those substances in true solution, is known as blood plasma. In 
this plasma the suspended substances are held. 

The material held in suspension in blood plasma amounts to 
about 60 per cent of the blood and consists of cellular bodies 
known as blood corpuscles, blood plates and blood dust. The 
most important of these bodies are the two forms of corpuscles 
known as red corpuscles or erythrocytes and white corpuscles or 
leucocytes. 

Red Blood Corpuscles or Erythrocytes. — The erythrocytes 
are cells which have lost their nucleus. In mammals they have 
the microscopical appearance of biconcave disks. They are of 
a yellowish color but in masses appear red. Their color is due 
to a protein known as hcemoglobin which permeates the real cell 
material known as the stroma. The stroma constitutes only 
5 to 10 per cent of the dry matter of the corpuscles, while 90 
to 95 per cent consists of haemoglobin. Two important con- 
stituents of the stroma are lecithin and cholesterol, which will be 
considered later (p. 280). 

Haemolysis and Hemagglutination. — Two properties of 
erythrocytes are of especial importance in connection with the 
action of toxins and the condition of immunity. When the 



MILK, BLOOD AND URINE 221 

blood plasma which holds the erythrocytes in suspension is 
made more dilute by the addition of water, an osmotic pressure 
is produced within the erythrocytes due to the rapid inward 
diffusion into the corpuscle of water from the plasma. This 
pressure may become strong enough to rupture the cell wall of 
the corpuscle, when the colored haemoglobin is discharged into 
the plasma, leaving the corpuscles colorless. This general 
action is termed hemolysis or taking, and may be produced also 
by certain substances, e.g. ether, chloroform, bile, the toxins 
of snake venom and of certain bacteria, and products produced 
in the body by immunization. The osmotic pressure of blood 
plasma is approximately equivalent to a 0.9 per cent solution 
of sodium chloride and in such a solution no haemolysis takes 
place. A salt solution of this strength is known as a physio- 
logical salt solution or normal saline solution. 

The second special property of erythrocytes is that of agglu- 
tination, or precipitation, when acted upon by certain substances. 
The action is called hemagglutination. 

Haemoglobin and Oxyhaemoglobin. — Haemoglobin, it will 
be recalled, was mentioned, in the discussion of proteins, as 
one of the conjugated proteins, consisting of a protein part (a 
histon called globin), together with an iron- containing colored 
part known as fazmochromogen. The erythrocytes are oxygen 
carriers, and it is this haemoglobin which is the essential con- 
stituent of red blood corpuscles in the performance of this 
function. Haemoglobin occurs in the venous blood, and when 
it comes in contact with inhaled air in the lungs it absorbs 
oxygen and is thereby converted into oxyhemoglobin in the 
arterial blood. In the blood capillaries of the cellular tissue the 
oxyhaemoglobin gives up its oxygen to the food nutrients, 
which are thereby oxidized and energy liberated, the oxyhae- 
moglobin in turn being reduced to haemoglobin. In this way 
the haemoglobin, a constituent of red blood corpuscles, acts as 
a carrier in conveying oxygen from the lungs to the muscle 
cells. This action probably rests in the iron component of the 
protein and is analogous to the bromine carrier property of 



222 ORGANIC AGRICULTURAL CHEMISTRY 

ferrous bromide. The amount of haemoglobin in fresh blood 
is about 14 per cent. As previously stated, the amount of 
blood is about 7.5 per cent of the body weight. A man of 68 
kilograms (150 lbs.) would, therefore, have approximately 5100 
grams of blood containing 714 grams of haemoglobin. The 
oxygen-absorbing power of haemoglobin has been determined 
as 1.34 c.c. oxygen per gram of haemoglobin. The total oxygen- 
carrying power of the blood of an adult man would, therefore, 
be about 950 c.c. Oxyhaemoglobin may be crystallized, and it 
has been found that the crystal form varies with different species 
of animals. 

The shape and size of erythrocytes vary with different ani- 
mals. In man the size is about 3 £ 0& of an inch, in the ele- 
phant 2tV^ °f an mcn J m the ox im of an inch, and in the 
musk deer 12 ^ 0Q . of an inch. 

The number of erythrocytes is very large and has been shown 
to vary with marked changes in condition. In the adult human 
male the number is about 5,500,000 per cubic millimeter, in 
the female about 4,500,000. Under abnormal conditions 
affecting the rate of oxidation in the tissues, as after physical 
exertion, or at high altitudes, the number has been found to 
increase to 7,000,000, and in pathological cases as high as 
11,000,000. Under conditions of decreased oxidation, as in the 
disease known as ancemia, the number has been found to fall to 
500,000. 

White Blood Corpuscles or Leucocytes. — The other cor- 
puscles of the blood, known as white corpuscles, or leucocytes, 
because they do not contain a color pigment, are larger than 
the red corpuscles and are characterized further by possessing 
a nucleus. They are not as numerous as the erythrocytes, 
varying from 5000 to 10,000 per cubic millimeter. This 
number varies still more widely under certain pathological 
conditions. The functions of the leucocytes is not fully estab- 
lished. They have been termed blood scavengers, as it is claimed 
that they destroy pathogenic organisms such as bacteria, 
either by devouring them, or by producing other substances 



MILK, BLOOD AND URINE 223 

which prevent their activity. It is also thought that they take 
part in the production of immune substances in the blood. 
Other theories are that they aid in the absorption of fats and 
peptones, that they take part in the process of blood coagula- 
tion, and that they maintain the protein content of the blood 
plasma. 

Blood Plasma. — The blood plasma, as we have stated, is 
the liquid portion which holds the corpuscles, plates and dust 
in suspension. In this blood plasma there are held in true 
solution both organic and inorganic substances. The amount 
of solid matter contained in the plasma is about 8.0 per cent. 
The organic constituents amount to about 7.0 per cent and the 
inorganic to about 1.0 per cent. 

The two most important organic constituents are glucose 
sugar and proteins. The former is in very small amounts, only 
about 0.1 per cent, but is very important, as it is the form in 
which carbohydrate food, and perhaps all food, is finally oxidized 
in the cells. The protein constituents are in larger amounts 
and are four in number, viz. (1) fibrinogen, (2) a nucleoprotein, 
(3) a globulin, and (4) serum albumin. Other organic constit- 
uents present in small amounts are enzymes, fats, lecithin, 
cholesterol, sarco-lactic acid, urea, uric acid and some others. 

The inorganic constituents of blood plasma include chlorides, 
carbonates, sulphates and phosphates of the metals sodium, cal- 
cium, magnesium, potassium and iron. 

Blood Serum. — When fresh-drawn blood is exposed to the 
air, the striking phenomenon termed clotting takes place. In 
this clotting of the blood one of the soluble protein constituents 
of the blood plasma, the fibrinogen, is converted into an in- 
soluble protein termed fibrin. This insoluble fibrin in separat- 
ing carries down with it the blood corpuscles and other sus- 
pended matter in the form of a thick clot. As this clot sepa- 
rates there is left a light yellow liquid known as blood serum. 
The serum differs from plasma in containing no fibrinogen. 
In it there are present, however, all of the other soluble con- 
stituents of the plasma. 



224 ORGANIC AGRICULTURAL CHEMISTRY 

Serum Albumin. — The most important protein constit- 
uent of serum is the albumin, which is like egg albumin in being 
soluble in water. In considering the absorption and metab- 
olism of protein food we stated that the absorbed products of 
protein digestion enter the blood and are metabolized into 
blood protein, which is then carried to the tissue cells, where 
oxidation takes place. Although it is not fully established, it 
is probable that the serum albumin is the form in which food 
protein is carried to the cells. If this is true, the relation be- 
tween serum albumin and food protein is of direct importance. 
The amount of serum albumin varies in different animals, and 
in man amounts to about 4.5 per cent. 

Fibrinogen and Fibrin. — The second protein constituent of 
blood plasma is the fibrinogen, which is a globulin soluble in 
dilute salt solutions such as the blood plasma. It is present in 
small amount, probably not over 0.4 per cent, in man. It is 
also a normal constituent of lymph. 

Clotting. — The special interest in connection with fibrino- 
gen is its relation to the characteristic clotting property of blood. 
This action takes place whenever fresh blood comes in contact 
with the air, and is the natural process by which the flow of 
blood from a wound is stopped, thus preventing too great loss 
of this important body fluid. The process of clotting is a 
complicated one, involving the action of several enzymes. It 
is not fully established, but the most generally accepted view 
in regard to the various steps may be given as follows. 

The leucocytes, or white blood corpuscles, together with the 
blood plates produce, probably with the aid of a kinase, or 
activator, a ferment known as prothrombin. This prothrombin 
is the zymogen of another enzyme, and when activated by cal- 
cium salts, present in the plasma, produces the enzyme called 
thrombin, or fibrin enzyme. Thrombin then acts directly upon 
the soluble protein fibrinogen, and the product is an insoluble 
protein called fibrin. The separation or coagulation of this 
insoluble protein forms the network or foundation of the blood 
clot, which contains also the solid suspended constituents of 



MILK, BLOOD AND URINE 225 

the blood, i.e. corpuscles, etc., which are held mechanically and 
carried down with the fibrin. 

If fresh-drawn blood is beaten rapidly with a bundle of fine 
twigs or of strings, the coagulating fibrin will be caught on the 
twigs, while most of the corpuscles remain in the serum. Blood 
so treated is called de-fibrinated. The fibrin so separated may 
be used for testing the color reactions of proteins or the diges- 
tible action of proteolytic enzymes. It is a white fibrous 
material and responds to all protein tests. 

Under normal conditions, freshly drawn blood will clot in 
from two to ten minutes, though the rapidity of clotting varies 
a good deal in different animals and is especially slow under 
certain pathological conditions as in fever. The separation of 
the clot from the serum takes place very slowly, requiring from 
ten to forty-eight hours. The time taken for clotting may be 
shortened very greatly by certain treatment and is often done 
in controlling hemorrhages. A solution of ferric chloride or 
alum applied to a fresh cut produces an almost instantaneous 
clotting. The natural clotting may be hastened or retarded 
by the injection of certain substances, e.g. calcium salts. In 
general an increase of carbon dioxide and decrease of oxygen 
causes blood to clot more slowly and vice versa. Snake venom 
and toxic albumin cause marked retardation in clotting ; and if 
blood is drawn into a solution of ammonium oxalate, it will not 
clot. 

The reason why blood does not clot until exposed to the air 
is not wholly explained, but is considered to be due to the 
presence in the normal blood of an anti-enzyme called anti- 
thrombin which prevents the action of thrombin upon fibrino- 
gen. It is also probably true that very little if any thrombin 
is present in the blood within the blood vessels, as the leuco- 
cytes do not yield prothrombin until the action of air causes 
them to disintegrate. 



226 ORGANIC AGRICULTURAL CHEMISTRY 

EXPERIMENT STUDY XXX 

Blood 
(i) Oxalated Blood. Secure some blood from a horse or cow and 
let it flow directly into a 10 per cent solution of ammonium oxalate. 
The blood will remain unclotted and may be examined under high 
power microscope for blood corpuscles. (See Hawk, " Practical Phys- 
iological Chemistry" (1913), p. 197, for plates showing corpuscles.) 

(2) Fibrin. Draw off another quantity of blood, 100-200 c.c, and 
immediately whip or stir it vigorously with some fine glass rods or a 
small bundle of twigs or a bunch of stout cord tied on to a stick and 
with loose ends like a mop. When clotting has been effected and the 
fibrin has adhered to the rods or string, remove the beater and wash 
the fibrin as clean as possible from all other material. Examine the 
fibrin as to general character and make the protein tests with it as in 
Experiment XVIII, 4. 

(3) Defibrinated Blood. The blood from which the fibrin has been 
removed may now be examined for blood corpuscles and for other 
constituents such as sugar, chlorides, etc. 

URINE 

Urine differs from milk in being considered as an excretion, 
not as a secretion. It is the medium by means of which the 
nitrogenous products of protein metabolism are removed from the 
body. When the food nutrients are oxidized in the cells, the 
carbon dioxide and water, resulting from the carbon and hydro- 
gen of the fats and carbohydrates and also from a portion of 
the carbon and hydrogen of proteins, is excreted in the exhaled 
breath. All of the nitrogen and some of the carbon and hydro- 
gen of the protein oxidation yield products which find their 
way into the urine and are excreted in this way. The nitrogen 
content of urine becomes, therefore, a measure of the protein 
metabolism in the animal body. The nitrogen compounds in 
urine are more or less complex compounds, containing carbon 
and hydrogen together with the nitrogen, and they consequently 
possess the possibility of being oxidized. This means that all 
of the energy of oxidizing proteins is not yielded in the cell 



MILK, BLOOD AND URINE 227 

where this oxidation takes place, but that some of it is still 
retained and locked up, as it were, in the urine excretion prod- 
ucts and thus lost to the body. This will be explained in 
detail when we study food values (Chapter XVII). 

Constituents 

Nitrogen Compounds. — The most important constituents of 
urine in connection with normal metabolism are the nitrogen 
compounds. The most abundant compounds of this class are 
urea, uric acid, creatinine and the purine bases; xanthine, etc. 
The chemical constitution and relationship of these com- 
pounds has been already considered, so far as is necessary, in 
Section I. 

Urea. — The chief constituent of urine and the principal 
nitrogen product of protein katabolism is urea. Under normal 
conditions of diet and health the urea represents about 88 per 
cent of the total nitrogen in urine. This relative amount may, 
however, be changed very decidedly by changes in the total 
amount of protein metabolized. Urea is more abundant in 
the urine of man and flesh-eating animals than in herbivorous 
animals. It is also present in most of the fluids of the animal 
body, as in blood, as already mentioned. In man the total 
amount per day is about 30 grams. As this represents about 
88 per cent of the total nitrogen in urine which, in turn, is the 
whole of the nitrogen of metabolized protein, it means that the 
total nitrogen metabolism per day is about 16.0 grams, equiv- 
alent to 100 grams of protein. As we shall find under food 
requirements this is the normal amount of protein required by 
man per day. 

Isolation and Determination. — The isolation of urea from 
urine is easily accomplished by converting it first into a nitric 
acid salt, crystallizing this, and then setting the urea free by 
the action of a weak base (barium carbonate). This will be 
described in the experiment following. The approximate 
determination of urea in urine is also easily made, and as the 



228 ORGANIC AGRICULTURAL CHEMISTRY 

accurate determination of total nitrogen in urine is a com- 
plicated chemical process, the former is used very largely as 
a clinical method for judging the protein metabolism of 
the body. This also will be considered in the experiment 
study. 

Uric Acid. — This compound, closely related to urea in its 
constitution (seep. 102), is an important constituent in man and 
other flesh-eating animals, though present in quite small amounts. 
The daily excretion is about 0.6 grams under normal conditions, 
and represents about 1.0 per cent of the total urine nitrogen. 
The amount varies greatly however under certain pathological 
conditions. The source of uric acid is the metabolism of a 
special group of proteins, viz. the nudeo- proteins, and in 
mammals is one of the minor products of metabolism. In 
birds, however, it is the chief nitrogenous metabolic product, 
being formed similarly to urea in mammals. 

Creatinine. — This nitrogen compound is present in urine to 
the amount of about 1.5 grams per day, equivalent to about 3.6 
per cent of the total urine nitrogen. It is an anhydride of 
creatine which is a normal constituent of muscular tissue. 
Creatine is related to urea through guanidine which is imino 
urea or 

/NH 2 
HN=C< 

X NH 2 

Ammonia. — About 3.0 per cent of the total nitrogen in 
urine is present as ammonia. The amount is, however, sub- 
ject to considerable variation, depending upon the relative 
amounts of acid and basic constituents of the food. If not 
held by acids in a stable form, it is converted into urea. The 
relative amounts of these two constituents are thus inter- 
dependent and in pathological cases have been known to be 
almost reversed. According to Sherman the amounts of the 
different nitrogen compounds in urine per day following a 
high protein diet are as follows : 



MILK, BLOOD AND URINE 



229 




Per Cent of Total 
Nitrogen 



Total nitrogen . . . 
Urea nitrogen . . . 
Ammonia nitrogen . . 
Uric acid nitrogen . . 
Creatinine nitrogen . . 
Undetermined nitrogen 



87.5 per cent 

3.0 per cent 

1.1 per cent 
3.6 per cent 
4.9 per cent 



Hippuric Acid. — This compound, it will be recalled (p. 92), 
is benzoyl amino-acetic acid. It is present in the urine of man 
in about the same amount as uric acid, 0.7 grams per day. It 
is much more abundant in herbivorous than in carnivorous 
animals. 

Pathological Constituents, Glucose. — Two important patho- 
logical constituents of urine should be mentioned. These are 
glucose and albumin. Under deranged metabolic conditions, 
the cause of which is not fully understood, the body loses its 
power of utilizing carbohydrate food by the oxidation of glu- 
cose. Under such conditions the glucose is excreted in the urine. 
The pathological condition in such cases is known as glyco- 
suria, and the particular disease when the condition is per- 
sistent is called diabetes mellitus. Glucose is never a constit- 
uent of normal urine, at least in amounts detected by ordinary 
chemical tests. Any positive test for glucose in urine is, there- 
fore, indicative of an abnormal condition. The qualitative 
and quantitative determination of glucose in urine is made by 
means of Fehling's solution, or some modification of it. The 
original Fehling's solution will not detect glucose in amounts 
less than about 0.1 per cent, and the action is also interfered 
with by creatinine, a normal constituent of urine. On this 
account, Benedict has suggested a modification of the solu- 
tion, which is not interfered with by creatinine and that will 
detect as little as 0.015 per cent. The solution is made as 
follows : 



3J0 ORGANIC AGRICULTURAL CHEMISTRY 

Benedict's Modified Fehling's Solution 

Copper sulphate 17.3 grams 

Sodium citrate i73-o grams 

Sodium carbonate 100.0 grams 

(anhydrous) 

Water to make 1000.0 c.c. 

Glucose is also sometimes tested for clinically by subjecting the 
urine to the action of yeast and measuring the carbon dioxide 
evolved. 

Albumin. — The presence of albumin in urine indicates a 
pathological condition termed albuminuria or nephritis. Bright' s 
disease is a particular form of the condition. The testing of 
urine for albumin, as for glucose, is therefore an important 
clinical operation. The test usually made depends upon the 
property of albumins to form insoluble compounds with mineral 
acids. It is known as Heller's ring test and is described in the 
experiment study. 

General Properties 

Human urine is a clear straw-colored liquid, becoming often 
considerably darker if of high specific gravity. The amount 
varies greatly with the amount of water that is drunk, but 
averages from 1000 to 1500 c.c. in twenty-four hours. It fre- 
quently becomes cloudy on standing, due to the precipitation 
of phosphates, especially if the urine is alkaline in reaction, which 
often occurs after a hearty meal. Normally urine is slightly 
acid in reaction. The specific gravity of normal urine is 1.015 
to 1.025. This may be greatly changed by large variations in 
drinking water. Excessive drinking of water may so dilute the 
urine as to lower its specific gravity to 1.003 and cutting down 
the supply of water may raise it to 1.04. Diabetic urine has a 
high specific gravity, but this alone does not indicate the disease 
unless the amount of water is considered. 



MILK, BLOOD AND URINE 23 1 

EXPERIMENT STUDY XXXI 

Urine 

(1) Determine the amount of urea in normal urine by means of the 
ureometer as in Experiment XIX, 1. 

(2) Isolation of Urea from Urine. Evaporate 2-3 liters of urine in 
a large evaporating dish in a hood until it is the consistency of sirup. 
Cool and add concentrated nitric acid as long as crystals form. 
Filter, with suction on a Buchner funnel. The crystalline product is 
urea nitrate. Recrystallize and decolorize to light straw color with 
potassium permanganate solution. Dissolve the urea nitrate in 
water and add barium carbonate as long as effervescence occurs. 
Filter off any excess of barium carbonate and evaporate the filtrate 
to dryness. Extract the dry residue with hot alcohol, filter, evap- 
orate the alcoholic extract to a small volume, cool, and allow the 
urea to crystallize out. Filter off the crystals of pure urea and 
examine them as in (1). 

y NH 2 /NH 2 -HN0 3 /NH 2 

0C< +HN0 3 ->OC< +BaC0 3 -»0(X +Ba(N0 3 ) 2 

X NH 2 N NH 2 X NH 2 

Urea in urine Urea nitrate Urea 

(3) Albumin, Heller's Ring Test. Place 5 c.c. of dilute egg albumin 
solution in a test tube or, better, a conical test glass. By means of a 
pipette lowered to the bottom of the test tube let an equal volume of 
pure concentrated nitric acid flow underneath the albumin solution 
so as to keep the two layers. Note the cloudy precipitate form at 
the junction of the two liquids. Repeat several times, diluting the 
egg albumin solution ten times at each successive trial. Note the 
delicacy of the test. This is used as a clinical test for albumin when 
present in small amounts in urine in cases of the disease known as 
Nephritis or B right's Disease. 

(4) Glucose. To a sample of urine add about 0.5 per cent of glu- 
cose, (a) Test the urine for glucose with Fehling's solution as de- 
scribed under glucose (p. 114). (b) Test similarly, using Benedict's 
modified Fehling's solution. (See Hawk, "Practical Physiological 
Chemistry," p. 329, for details in regard to this test.) (c) Dilute the 
urine with an equal volume of fresh urine five times and repeat with 
each solution. 



CHAPTER XIV 
PLANT PHYSIOLOGY 

PLANTS AND ANIMALS COMPARED 

In the discussion just concluded we have endeavored to 
show how the living cell, and thus the organism as a whole, 
utilizes food materials for the production of the energy neces- 
sary for its living processes, and by a study of the animal body 
to explain the chemical changes that take place in the trans- 
formations of this food until it is finally oxidized and the energy 
liberated. 

We shall now study the plant organism to find out how, by 
means of its distinctive physiological processes, the three essen- 
tial organic food constituents, carbohydrates, fats and proteins, 
are formed and the plant structure built up. 

Similarity of Plants and Animals. — In our study of animals 
and the physiological processes by which they utilize their 
food we grouped the chemical reactions taking place under two 
heads, viz. digestion and metabolism. Digestion may be con- 
sidered as a preliminary change taking place in the food material 
outside of the real body proper, that is, in the digestive tract. 
By means of this change the mixed food substance is brought 
into the particular condition necessary for absorption and 
metabolism. After the digested food material is absorbed into 
the body proper it undergoes more or less complicated changes 
embraced in the term metabolism. During the period of 
metabolism the food performs its two functions, viz. it is built 
up into body substance or it is oxidized and yields energy. 
These two functions eventually become one, for the body sub- 
stance, in most part, is, sooner or later, metabolized further 
and finally oxidized with the liberation of energy. 

232 



PLANT PHYSIOLOGY 233 

In the animal this liberation of energy is the predominating 
function of the organism or, as we may say, energy is the net 
result of the animal physiological reactions. Animals may be 
characterized therefore as energy-liberating organisms. 

The energy food of animals consists of three classes of com- 
pounds, viz. carbohydrates, fats and proteins. These three 
complex compounds, containing carbon, hydrogen, oxygen and 
nitrogen, on oxidation, are broken down into simpler com- 
pounds, viz. carbon dioxide and water, which are excreted 
mostly in the breath, and nitrogen compounds derived from the 
proteins only, which are excreted in the urine. In this break- 
ing down by oxidation the potential energy stored or conserved 
in these complex compounds is liberated as kinetic energy of the 
living animal. The reaction illustrating such changes is that 
of the oxidation of glucose as it takes place in the animal cell, 
viz. : 

C 6 Hi20 6 + 6 2 -> 6 C0 2 + 6 H 2 + energy 

Glucose 

The energy thus liberated as kinetic is manifested in two 
forms, (1) as animal heat, (2) as muscular work. As the animals 
with which we have to do are warm-blooded organisms, a con- 
siderable amount of energy is required to supply the necessary 
heat. The expenditure of energy as muscular work is also 
large because such work is continual, either as voluntary or 
involuntary, so long as life exists. In man it has been found 
that the energy so expended for body heat and simply the 
involuntary muscular work of the body at rest amounts to about 
1600 to 2000 Calories per day. 

Now all that we have thus reviewed as to the relation between 
food and energy is true of the plant organism as well as the 
animal, except as to amount. In animals the expenditure or 
liberation of energy is the chief or predominating reaction, 
while in plants it is not the predominating reaction. 

The plant cell or the complex plant organism of many such 
cells is of exactly the same nature in its living processes as the 
animal. For the maintenance of life energy must be set free, 



234 ORGANIC AGRICULTURAL CHEMISTRY 

and in both plants and animals this energy is supplied by the 
same food materials, carbohydrates, fats and proteins, which 
undergo analogous metabolic reactions. As has been stated, 
however, the entire function of food is the formation of body 
substance and the liberation of the energy necessary for life. We 
have given an example as to how much this energy amounts 
to in man. In plants, while we cannot express the results in 
definite figures, we can readily conceive of the magnitude, in 
both body substance and energy, if we think of one of our 
large trees. The mass of body material that has been built up 
and the amount of energy expended to lift such a mass to the 
height attained and to maintain it in position must both be of 
very great magnitude. This material and this energy are 
both supplied by the food of the plant. 

In the animal body we can easily measure and control the 
food supply and we can also determine, to a large extent, the 
energy expended. In plants, on the contrary, it is impossible 
to do this and on this account the study of food metabolism 
and the relation between food and energy has been almost 
entirely studied in connection with animals. For this reason, 
and because it is necessary first to understand this food and 
energy relation of living organisms, we began our physiological 
study with animals rather than with plants. 

Too much emphasis cannot be placed upon the fact that the 
animal and the plant, as living organisms, are essentially the 
same. Both build their body substance and obtain the energy 
of their living processes by the metabolism of food consisting 
of carbohydrates, fats and proteins. 

In connection with animals we have spoken of the inorganic 
food materials consisting of certain inorganic salts. Some of 
these are essential to the building of certain parts of the body 
substance, while others act physiologically in the fluids of the 
body. They are undoubtedly just as essential as the organic 
foods, but they are not directly related to the energy supply 
of the body. They are also used in much smaller amounts 
and, being present in sufficient quantity in most foods, they do 



PLANT PHYSIOLOGY 235 

not appear to be so important. In plants the inorganic food 
materials obtained from the soil are essential as building ma- 
terial, and as physiological activators, but here also they do 
not contribute directly to the energy of the plant. Because, 
however, the supply of these materials in the soil is liable to 
exhaustion and, because the supply of organic food materials as 
manufactured by the plant itself is practically limitless, these 
inorganic foods have a much greater relative importance in 
plants than in animals, and are usually referred to when the 
term plant food is used. 

Differences between Plants and Animals. — If then animals 
and plants are alike, as living organisms in the relation of food 
and energy, wherein lies the essential difference that char- 
acterizes them as plants and as animals? 

In the discussion which follows we must emphasize the 
point that we shall speak of general facts and conditions as 
pertain especially to the higher green plants with which our 
study is related. In considering all of the varying forms of 
plant life, from the lowest to the highest, many different condi- 
tions exist, and plant physiology as a whole must consider them 
all and correlate the facts into a system, but for our purpose 
only the main general facts are essential and these we shall 
obtain from a study of the higher plants. 

Exothermic and Endothermic Reactions. — All chemical 
reactions are of two kinds in their relation to energy. One 
kind of reaction liberates or expends energy or is, as we term 
it, exo-thermic (gives out heat). The other kind absorbs or 
conserves energy and is termed endo-thermic (takes in heat). 
The exothermic reaction converts potential energy into kinetic, 
while the endothermic reaction converts kinetic energy into 
potential. The exothermic reaction is in general true in cases 
in which a complex compound is broken down into simpler 
ones, especially if the reaction involves additional oxygen, that 
is, if the compound is oxidized. Such a reaction is typified by 
the oxidation of glucose, as given above, yielding carbon dioxide 
and water as the products, with the liberation of energy. Re- 



236 ORGANIC AGRICULTURAL CHEMISTRY 

actions of this kind are those by which the living organism 
obtains the energy necessary for its life and, as we have shown, 
take place in both plants and animals. 

Endothermic reactions are in general those in which simpler 
compounds are synthesized or built up into complex compounds. 
These may be typified by the reverse of the reaction just men- 
tioned, viz. 

6 C0 2 + 6 H 2 + energy -> CeHisOe + 6 2 

Such a reaction involves the absorption of kinetic energy and 
the conversion of it into potential energy which is stored or 
conserved as such in the complex compound formed. At the 
same time oxygen is set free. These endothermic reactions also 
occur in living organisms, and in animals may be illustrated by 
the known conversion of carbohydrates into fats with the 
storage of energy and the evolution of oxygen. In plants we 
shall find that the endothermic reaction above given takes 
place in a wonderful way in the synthesis of glucose from 
carbon dioxide and water. 

Animals Liberate Energy. — We have mentioned the fact 
that in animals the reactions which liberate energy, the exother- 
mic reactions, are predominant. 

Plants Store Energy. — In plants, on the contrary, the 
predominating reactions are not the exothermic or energy 
liberating, but are endothermic or energy storing. In other 
words, the net result of plant physiological reactions is the 
storage of energy. 

This, then, is the characteristic difference between animals 
and plants. Both, as living organisms, require complex com- 
pounds as food material, which by oxidation break down into 
simpler compounds with the liberation of energy. Both also 
build up simpler compounds into more complex with the storage 
of energy and the evolution of oxygen. In animals, however, 
the liberation of energy is predominant, that is, animals are 
energy liberators; while in plants the storage or conservation of 
energy is predominant, that is, plants are energy storers. This 



PLANT PHYSIOLOGY 237 

characteristic difference may be stated in another way. Ani- 
mals utilize food that is brought to them from the outside, 
they cannot synthesize their own food. Plants, on the other 
hand, manufacture or synthesize their own food. 

PHOTOSYNTHESIS 

We shall now study the way in which plants store energy in 
building up complex compounds out of simple ones, these 
complex compounds so produced being the food of the plant 
itself. The compounds concerned in this energy-storing process 
are, as we have repeatedly said, the three classes, carbohydrates, 
fats and proteins, and the material out of which they are con- 
structed consists of the two common substances, carbon dioxide 
and water, together with nitrogen obtained mostly from the 
soil. How, then, is the plant enabled to carry out this won- 
derful synthesis? 

Source of Energy. — As we have previously explained, the 
endothermic reaction involved in the synthesis of carbohydrates 
from carbon dioxide and water requires the addition of energy. 
Where does the plant get this energy? The energy by means 
of which plants are able to carry out this reaction comes directly 
from the sun. Through this endothermic reaction the kinetic 
energy of the sun is converted into the potential energy of complex 
organic compounds and stored in the plant. This kinetic energy 
reaches the plant through the action of the sunlight and acts, 
therefore, only during daylight and only upon those parts of the 
plant which are above ground and exposed to the light. 
Furthermore, generally speaking, only those plants known as 
green plants, or phanerogams, are able to thus utilize the energy 
of the sun. It has been shown experimentally that other 
forms of energy can produce this synthesis in plants, but it 
is not necessary to discuss them. In normal living green 
plants it is certain that much the greater part, if not all, of the 
energy connected with this synthesis is the radiant energy of 
the sun. 



238 ORGANIC AGRICULTURAL CHEMISTRY 

Chlorophyll Bodies and Chlorophyll. — This power of plants 
to utilize the energy of the sunlight is dependent upon the 
action of certain bodies known as chloroplasts or chlorophyll 
bodies. These chlorophyll bodies have associated with them 
a green pigment known as chlorophyll. It is this chlorophyll 
which gives to the aerial parts of plants their green color 
and which characterizes them as green plants. Much has been 
learned of late years in regard to the chemical character of 
chlorophyll, but its exact nature is still a question, and it will 
not be desirable to enter into any discussion of it here. 

These two agencies always act together, the chlorophyll as 
the assimilatory pigment, and the chloroplasts as the mechanism 
of assimilation. Thus through the action of the chlorophyll in 
its relation to sunlight some of the energy of the sun is used by 
the chlorophyll bodies in bringing about a chemical reaction of 
endothermic character which results in the synthesis in the 
plant of complex organic compounds which have stored up in 
them as potential the kinetic energy derived from the sun. 
These compounds then become the energy food of the plant 
itself. Because light is necessary for this synthesis it is known 
as photosynthesis. The simple compounds involved in this photo- 
synthesis are carbon dioxide and water. The former is present 
in the atmosphere and the latter in both atmosphere and soil. 

Products of Photosynthesis. — We have stated that the 
final products of this synthetic reaction are carbohydrates, fats 
and proteins. We can ask, however, what is the first or direct 
product? This question we are unable to answer definitely. 
We do not know positively what individual compound is first 
formed by this synthesis, nor can we even state absolutely 
whether it is carbohydrate or fat or protein. 

We have written the endothermic reaction for the production 
of glucose from carbon dioxide and water as : 

6 C0 2 + 6 H 2 + energy -> C 6 Hi20 6 + 6 2 

This is the reverse of the exothermic reaction whereby glucose 
is oxidized to carbon dioxide and water with the liberation of 



PLANT PHYSIOLOGY 230 

energy. In this reaction we can measure exactly the amount 
of the energy liberated. Results of such measurement show 
that one gram of glucose, when completely oxidized, yields 
4.1 Calories of energy. We write this reaction, then, 

CeH^Oe + 6 2 -> 6 C0 2 + 6 H 2 + energy 

1. o g. 4.1 Cal. 

We know, also, that by the laws of chemical equilibrium the 
energy required in the synthesis of glucose from carbon dioxide 
and water is exactly equivalent to the energy liberated when 
glucose is completely oxidized. Furthermore, the synthesis of 
glucose from carbon dioxide and water has actually been ac- 
complished in the laboratory, though the reaction involves 
several steps and is not so simple and direct as we have written 
it. 

We stated in our discussion of glucose and fructose sugars 
(p. 113) that they have both been synthesized in the laboratory 
horn formaldehyde. Also, in speaking of formaldehyde (p. 43), 
we said that it had been synthesized from carbon dioxide and 
water. If we write the chemical reaction expressing these 
facts, we have : 

CO2 + H 2 -> H-CHO + 2 

Formaldehyde 

6H-CHO->C 6 H 12 6 

Formaldehyde Glucose 

The above formation of formaldehyde from carbon dioxide 
and water has been claimed by several investigators in plant 
physiology to take place when the two substances are acted 
upon by sunlight in the presence of a catalyzer. This catalyzer 
may be either an inorganic substance like a uranium salt, or it 
may be an extract of green leaves. It has also been claimed 
that in green plants formaldehyde is present, though it is so 
rapidly removed, probably by polymerization, that it does not 
collect. It is possible, too, that the synthesis is not in one direct 
step but that intermediate products, such 2& formic acid, hydrogen 
peroxide or carbon monoxide, may be produced. At any rate it 



240 ORGANIC AGRICULTURAL CHEMISTRY 

seems probable, and is pretty generally accepted, that formalde- 
hyde is first produced and is immediately further transformed 
into carbohydrate. Fincke, 1 however, claims that the forma- 
tion of glycolic aldehyde, CH 2 OH — CHO, as an intermediate 
product is in closer agreement with known facts. 

One further point in connection with this step in the photo- 
synthetic process is that the other product of this laboratory 
synthesis, viz. oxygen, is also the other product of the reaction 
as it takes place in plants. When carbon dioxide is assimilated 
by plants, oxygen is given off, and this evolution of oxygen is 
directly proportional to the photo synthetic activity. The absorp- 
tion of carbon dioxide and evolution of oxygen by plants was 
originally taken to indicate that the life process in them was 
directly the opposite of that in animals. This we now know 
to be wrong, for, as we have shown, the living process of the 
cell and the utilization of its food for the liberation of energy, 
with the excretion of carbon dioxide as one of the products of 
the oxidation reaction, is alike in both plants and animals. 

The other part of the double reaction representing the synthe- 
sis of glucose from carbon dioxide and water, viz. the polymeriza- 
tion of formaldehyde to glucose, is one of which there is no 
doubt as a laboratory reaction and also one that is perfectly 
possible in the living plant. 

We must emphasize the fact, however, that because we have 
a right to express by these reactions a known laboratory synthe- 
sis, this does not establish the fact that the same synthesis takes 
place in plants. Other reactions have been established in the 
laboratory which make it also possible that from the same 
original substances fats may be synthesized and even proteins, 
provided nitrogen compounds are supplied from the soil. All 
plant physiologists and chemists have not yet accepted it as 
proved that formaldehyde is present in plants nor that it is 
the actual intermediate product in carbohydrate synthesis. 
We know beyond question this much only : (i) The end prod- 
ucts of the reaction of photosynthesis are on the one hand 

1 Fincke, Z. Nahr. Genuss., xxvii, 8 (1914)- 



PLANT PHYSIOLOGY 241 

carbon dioxide and water and on the other not only carbohydrates, 
but also fats and proteins; (2) the kinetic energy of sunlight is 
necessary to produce the synthesis; (3) oxygen is evolved. Still, 
taking everything into consideration, it seems probable, as 
supported by laboratory syntheses and by the well-supported 
claim of the presence of formaldehyde in plants, that in plants 
the process of photosynthesis results first in the synthesis of 
a non-carbohydrate compound, formaldehyde, from carbon di- 
oxide and water at the same time setting free oxygen which is 
given off by the plants, the formaldehyde then polymerizing 
to the formation of glucose sugar which is thus the first of the 
essential organic constituents to be formed as the direct product 
of photosynthesis. This view, it may be said, is more generally 
accepted than any other. 

FUNCTION OF THE PRODUCTS OF PHOTOSYNTHESIS 

Accepting, then, this view that the carbohydrate glucose is 
the first essential compound formed, we still have the fact that 
the final result of photosynthesis as a whole is the formation of 
the three energy-storing substances, carbohydrates, fats and 
proteins. All of these compounds are formed in the leaves 
and other green parts of plants and serve as food material for 
the plant itself, being in a condition analogous to that of digested 
and absorbed food in animals. Let us now take up separately 
these three groups of compounds which, either directly or in- 
directly, are the products of photosynthesis, and follow them in 
the fulfillment of their function as plant food. 

Carbohydrates 

This group of compounds is more abundant in plants than 
are fats or proteins. As an energy food for the plant itself we 
can hardly say that the carbohydrates are more important 
than the others, but they are used more abundantly as build- 
ing material for the plant body. This is in accord with their 
presence in greater amounts in most parts of the plant. 



242 ORGANIC AGRICULTURAL CHEMISTRY 

Carbohydrates Present in Plants. - The more common 
members of the carbohydrate group found in plants may be 
given as follows: 

Hexose monosaccharoses, 

Glucose — Grape sugar 

Fructose — Fruit sugar 
Disaccharoses, 

Sucrose — Cane sugar 

Maltose — Malt sugar 
Polysaccharoses (not sugars), yielding hexoses, 

Starch 

Cellulose 

Dextrin 

Inulin 
Polysaccharoses, yielding pentoses, 

Pentosans 

We find thus in plants all three of the main classes of this 
group, viz. simple sugars or monosaccharoses, double sugars or 
disaccharoses and compound sugars (non-sugar in character) or 
polysaccharoses. All of these which are not hexoses themselves 
are related to them and yield them on hydrolysis. In addition 
to these we have also the polysaccharoses yielding pentose 
sugars, i.e. the pentosans. In fact only three carbohydrates, 
viz. glycogen, lactose and galactose, are found either exclusively 
in animals or to a larger extent in animals than in plants. This 
characterizes plants as the main and, with the exceptions cited, 
the only source of the carbohydrates. 

Where, then, in the plant, do we find these different com- 
pounds and how do they act as food ? In the leaves and other 
green parts we find two of these carbohydrates in such conditions 
that we are inclined to believe they are directly produced by 
photosynthesis. These two are glucose and starch. 

Metabolic Transformations. — From our chemical study of 
the carbohydrates we see that the relationship of the entire 
group is such that in the living plant there is possible a con- 



PLANT PHYSIOLOGY 243 

tinual transformation from one to the other. The chemical 
reactions involved require in most cases simply the loss or 
addition of the elements of water. These reactions are peculiar, 
also, in being brought about through the agency of enzymes 
which in many instances are known to be capable of producing 
a reversible reaction. In plants, water and enzymes are both 
abundant, so that there is nothing strange or improbable in the 
belief that here the various members of the carbohydrate group 
are constantly undergoing transformations back and forth 
into each other. For example, glucose and fructose may yield 
sucrose, glucose may yield maltose and then starch or cellulose, 
and vice versa in each case. Not only are such transformations 
possible theoretically, but direct experiment has proved that in 
many instances they actually do occur. If then glucose is the 
first essential constituent that is formed as a product of photo- 
synthesis, all of the other carbohydrates may be derived from it by 
metabolic changes. 

Sugars. — In all plant sap and juices, sugars are present and 
oftentimes several of them, not only monosaccharoses but also 
disaccharoses. Thus in fruit juices glucose, fructose and sucrose 
are found, while in plant sap sucrose is the sugar usually present. 

Translocation Material. — As sugars are the soluble car- 
bohydrates, all of the insoluble carbohydrates, starch in par- 
ticular, must be converted into one of the sugars in order to 
be possible of translocation from one part of the plant to another. 
Also, as all carbohydrates, used as building material or as cell 
food, must be translocated throughout the plant organism to 
all the various cells, the sugars are the particular form of car- 
bohydrates thus used. 

Cell Food. — In plants, as in animals, glucose is the form in 
which all carbohydrate food, and perhaps all food, is finally 
oxidized to yield energy. In plants, however, the production of 
energy is of much less relative magnitude than in animals, and 
not all of the glucose and other soluble sugars are required to 
be used as energy food. The greater part of these compounds 
is used in the plant as intermediate translocation material for 



244 ORGANIC AGRICULTURAL CHEMISTRY 

the building up of body substance or for storage as reserve food. 
The sugars are carried by the sap to all of the plant cells, and 
in the cells they undergo metabolic changes whereby they yield 
energy, form body substance or are converted into reserve food. 

Starch. — In two localities, in particular, do we find the sugar 
glucose thus metabolized into the polysaccharose starch. 

Reserve Food. — In both of these places the starch is reserve 
food. In the leaves of plants starch is always present. In 
fact it is so universally present here and follows so closely the 
photosynthetic activity that it was long believed to be the 
direct product of photosynthesis. It is probable, however, 
that glucose is first formed and the starch then produced by 
enzymatic action, involving loss of water and condensation or 
union of the unit glucose molecules into larger starch molecules. 
Though starch is constantly being thus formed in the leaves, it 
does not accumulate but is continually reconverted into maltose 
or glucose and carried away by the plant sap. This is clearly 
shown by the disappearance of the starch in leaves during 
darkness, when photosynthesis is not going on. In the morn- 
ing, following the darkness of night, practically all starch has 
left the leaves. This conversion and translocation of starch in 
the form of glucose is being carried on during the day as well 
as during the night, but as new starch is being continually 
formed at the same time, the translocation does not show as 
well as at night. The conversion of glucose, the product of 
photosynthesis, into starch which is immediately reconverted 
into glucose for translocation is quite closely analogous to the 
process in animals whereby absorbed carbohydrate food in the 
form of glucose, fructose or galactose is converted into glycogen 
in the liver and the glycogen then continually reconverted into 
glucose and sent out in the blood to all parts of the animal. 

Diastase and Maltase. — The conversion of starch in the 
leaves into glucose is brought about by enzymes known as 
diastase and maltase. These two enzymes convert starch first 
into maltose sugar and then into glucose. The starch in the 
leaves thus acts as a temporary reserve material very like the 



PLANT PHYSIOLOGY 245 

glycogen in animals. The glucose and maltose formed from 
the starch which in turn was formed from photosynthesized 
glucose, is carried by the sap throughout the plant, where it 
undergoes further metabolism, as previously stated. 

Part of this glucose is carried to other organs of the plant, 
viz. the seeds, tubers, roots, etc., which are reserve organs for 
the storage of starch food. In these reserve organs the sugars 
are again converted into starch and here the starch acts as re- 
serve food for renewed growth in the germ, buds, twigs, etc. 

Germination. — Roughly speaking, the seed of a plant con- 
sists of a germ which is surrounded by a reserve supply of food 
on which the new plant lives for the first period of its life. 
This reserve food consists of all three of the essential organic 
constituents, carbohydrates, fats and proteins, and also in- 
organic constituents or salts. The carbohydrate food in the 
seed consists usually of starch, though this may be replaced by 
sugars, reserve cellulose or inulin. When the germ begins to 
grow these food materials are gradually assimilated. 

In order to be used as food by the developing germ the starch 
is again hydrolyzed into maltose and glucose. This hydrolysis 
is brought about by the same enzymes as are active in the 
leaves, viz. diastase and maltase. This diastase of the seed, 
while considered to be the same enzyme as is present in the 
leaves, acts somewhat differently physically ; and to distinguish 
between the two the one in the seed is called diastase of secretion 
and the one in the leaves diastase of translocation. 

The isolation of diastase and maltase from germinating seeds 
and their hydrolytic action upon the starch of the seed, yield- 
ing glucose, has been fully established experimentally. In fact 
both the enzyme maltase and the sugar maltose, or malt sugar, 
upon which it acts, derive their names from the fact that they 
are present in, and can be easily isolated from, malt, which is 
germinated grain, usually barley. 

Thus we see that one of the results of carbohydrate synthesis 
in green plants is to produce food material either for the plant 
itself or for the germ of its offspring. 



246 ORGANIC AGRICULTURAL CHEMISTRY 

EXPERIMENT STUDY XXXII 

Action of Diastase on Starch 

(a) Extract 50 grams of finely ground malt (germinated barley) with 
warm (25°-3o° C.) water. Filter and test filtrate for reducing sugars 
(maltose or glucose). Ferment this nitrate with yeast until all fer- 
mentable sugars (maltose and glucose) have been converted into 
alcohol. Filter again if necessary and ret est for reducing sugars. 
No test should be obtained. Make a little starch paste, add the 
nitrate to this paste, and keep at 35 C. After a day test for starch 
and reducing sugar. 

(b) Prepared diastase may be used instead of the extract of malt if 
desired. 

Building Material. — We have discussed thus far two of the 
functions fulfilled by the photosynthesized carbohydrates, viz. 
(1) in the form of soluble sugars, probably always as glucose, 
to furnish the plant cells with food material for oxidation and 
the liberation of the energy of the living processes. (2) To be 
converted into starch as a temporary reserve material in leaves 
or as a reserve food for the germ of the plant's offspring in the 
seed, tuber, root, etc. 

One more function fulfilled by photosynthesized carbohy- 
drates is to be mentioned in more detail, viz. the conversion of 
it into material out of which the body substance of the plant 
is built. This building of body material is the second distinct 
function of food. 

In our study of animal food and nutrition we defined food, 
more especially the organic food, as any substance which 
taken into the body is used to build body material or to yield 
energy. Nutrition embraces all of the processes by which these 
functions are performed. The changes involved constitute 
metabolism, which is either constructive (anabolism) or destruc- 
tive (katabolism) . The result of anabolism is the building of 
body material which may be either temporary or more or less 
permanent. The result of katabolism is the yielding of energy. 
The metabolic changes which we have been considering in 



PLANT PHYSIOLOGY 247 

plants, following the photosynthesis of carbohydrates, have 
been mainly katabolic in their final results. We shall now 
consider those metabolic changes in carbohydrate material 
that are anabolic. 

Cell Wall. — We have spoken of the fact that the plant cell 
contains all three of the essential organic compounds, carbo- 
hydrates, fats and proteins, as constituent parts of the cell 
protoplasm. In addition to the cell protoplasmic contents we 
have the cell wall, and this consists largely, if not wholly, of 
carbohydrates in the form of cellulose. In all cases it is pro- 
duced by the conversion of the translocated sugars into cellulose, 
by reactions undoubtedly similar to those by which starch is 
formed in leaves and seeds. 

Cellulose. — In the young living cells of plants the cell wall 
is probably pure cellulose and it is somewhat different in char- 
acter from the cellulose of mature and old cells found in the 
stems, branches and trunks of the plant. Oftentimes the 
cellular structure takes on peculiar forms and produces the 
fiber which is contained in the boll of the cotton plant and in 
the stems of grasses, flax, hemp, etc. As the plant grows, 
especially in the case of large trees, the pure cellulose of the 
young cell walls becomes thicker and harder, due to the im- 
pregnation with gums, resins, lignins, pectins, pentosans, etc. 
Cell walls thus hardened give to the cellular structure the 
character of wood, which is much tougher and stronger than 
young cellular structures. In all these cases, whether in young 
living cells or in old woody cells, the cellulose of the cell wall is 
truly the building material of the plant and is not reserve food 
material. It is into such building material that a great part of 
the photosynthesized carbohydrates is eventually metabolized. 
When we consider the immense amount of cellulose thus formed 
in the case of large trees, and realize that while the plant is 
forming all of this body substance, it is, at the same time, using 
photosynthesized carbohydrates as direct energy food for the 
cells and also forming large amounts of reserve starch food, 
we get some idea of the magnitude of the process of photo- 



248 ORGANIC AGRICULTURAL CHEMISTRY 

synthesis. All of this food, representing both the energy and 
the body substance, is synthesized from the two simple com- 
pounds carbon dioxide and water by means of the energy of the 
sun through the agency of the chlorophyll bodies and chlorophyll. 

Fats and Proteins 

In the preceding discussion we have considered in detail 
simply the carbohydrates. The cell substance, however, con- 
tains all three of the essential organic compounds, and all three 
of them serve together as energy food. 

Synthesis of Fats and Proteins in Plants. — Though it is 
not absolutely proved, it is generally accepted that neither 
fat nor protein is a direct product of photosynthesis. The 
fact that, while the most important protein formation takes 
place in the leaves of plants, this formation is not connected 
with the activity of either chlorophyll or light, is evidence that 
protein is not thus formed. The synthesis of protein in leaves 
takes place in the absence of both of these agencies if there is 
present in the soil an abundant supply of soluble carbohydrate 
food together with nitrate nitrogen. 

If then, as we believe, the first product of photosynthesis is 
carbohydrate, both fat and protein are produced from this 
carbohydrate by metabolic change. We know that in animals 
the metabolic conversion of carbohydrates into fat is a fact. 
A similar metabolism in plants is entirely probable and is, in 
fact, definitely established by experimental study of the rela- 
tion between these two constituents. 

As fats are non-miscible with water they are unable to be 
translocated as such in the plant sap, but it has been shown that 
when they are in the form of fine emulsions they may be carried 
in the sap to the reserve organs. It is probable, however, that 
the greater part of the fat present in seeds has not been brought 
there by translocation, but has been formed in the seed directly 
by the metabolism of carbohydrates. In this metabolism 
different carbohydrates may take part, for it has been shown 



PLANT PHYSIOLOGY 249 

that an increase in fat may be accompanied by a decrease of 
either glucose or starch and in some cases of the hexahydroxy 
alcohol, mannitol. In the protoplasmic cell contents fats are 
present in the form of small globules. 

Location of Fats. — Fats, including in this term both fats 
and oils, occur in plants mostly as reserve food in the seeds. 
Waxes, on the other hand, occur principally in the vegetative 
organs, where they serve as protective material against drouth 
and cold. Fats are also found in smaller amounts in the 
vegetative organs and may likewise be protective. In most 
plants fats are not so abundant as carbohydrates. A few 
exceptions to this are oil-bearing seeds such as castor-oil bean, 
cottonseed, flaxseed and most nuts except chestnuts. 

Location of Proteins. — Protein, like fat, while occurring as 
an essential constituent of cell protoplasm and serving as 
energy food, is found mostly as a reserve food in seeds. It is 
synthesized originally in the leaves, as just stated. As it is 
found stored in seeds it is generally somewhat localized in the 
layer just beneath the outside, as in the aleurone layer in wheat 
grain. In the seed the protein together with the other con- 
stituents is used as food for the developing germ. 

Source of Nitrogen. — In the metabolism of photosynthesized 
glucose or other carbohydrate compounds into protein it is, of 
course, only the carbon-hydrogen- oxygen portion of the protein 
that can be supplied by the carbohydrates. The nitrogen of 
plant protein is derived from another source. In most plants 
the source of nitrogen is the soil, where it occurs principally in 
the form of nitric acid salts or nitrates. In this form the nitrogen 
is taken up by the plant roots and translocated to the cells. 
Here it meets with the carbohydrate cell food, and the two 
materials become metabolized into protein. In the case of 
other forms of nitrogen which are present in the soil, e.g. am- 
monium salts and organic nitrogen compounds (humus, etc.), 
these are converted by bacterial action into nitric acid nitrogen. 
The organic nitrogen compounds, consisting mostly of dead 
protein or protein residues, such as amino compounds, urea and 



250 ORGANIC AGRICULTURAL CHEMISTRY 

other urine constituents, are first decomposed into ammonia. 
This ammonia and other ammonium salts of whatever origin 
are probably in greater part then oxidized to nitric acid. This 
oxidation of ammonia to nitric acid takes place in the presence 
of atmospheric oxygen in the soil through the action of aerobic 
bacteria. The reaction may be represented in its simple form 
as follows : 

NH 3 + 2 2 + bacteria -> HN0 3 + H 2 

The nitric acid thus formed unites with bases in the soil, form- 
ing nitrates, e.g. potassium, sodium, ammonium, calcium, 
magnesium nitrates. In the form of these compounds, the 
nitrate nitrogen is taken up by the plant and metabolized into 
protein as above explained. It has been definitely proved, 
however, that plants can utilize ammonia nitrogen directly and 
also nitrogen in the form of urea or other amino compounds. 
To just what extent such nitrogen is utilized has not been 
established. 

One other source of nitrogen is of especial importance, but it 
applies only to certain plants, so far as is known only legumes 
such as clover, pea, bean, etc. In these plants there are present 
on the roots nodules containing bacteria which possess the 
characteristic property of assimilating free nitrogen from the 
air and converting it into protein nitrogen. 

Nitrogen Cycle. — The cycle of changes through which the 
element nitrogen passes in its existence in the atmosphere, soil, 
plants and animals is exceedingly interesting. Nitrogen, phos- 
phorus and sulphur are the only ones of the essential constituents 
of the soil food of plants which are converted into organic or 
energy food of the plant. The other more important plant 
food constituents, obtained from the soil and present also in 
fertilizers, are potassium and some others such as calcium, 
magnesium and iron. While compounds of these elements must 
be considered as true plant food, they are not energy food and 
should always be termed the soil food of plants as distinguished 
from their cell food or energy food. Their action is not fully 



PLANT PHYSIOLOGY 251 

understood, but they probably either contribute material for 
the formation of protein or act physiologically in connection 
with some of the metabolic changes which we have been dis- 
cussing. The general discussion of the questions connected with 
the plant's soil food constituents belongs properly to the 
study of soils and fertilizers in inorganic agricultural chemistry. 
As the nitrogen of the soil food of plants is, however, directly 
connected with the organic or energy food materials of plants, 
a further consideration of it is not out of place in our present 
study. 

Fixation of Atmospheric Nitrogen. — The ultimate source of 
all nitrogen is the atmosphere, where it is present in large amount, 
about 80 per cent. 

In just what way this atmospheric nitrogen first entered the 
cycle connected with living organisms is not certain, nor is it 
desirable for us to discuss the question at length. Three possible 
ways have been suggested by which nitrogen from the air could 
have entered the soil. 

(1) By the decomposition of metallic nitrogen compounds, 
e.g. the nitride of boron (BN). Such compounds were doubt- 
less formed when the surface of the earth cooled. On later 
decomposition with water, ammonia would be formed, and this 
could then have been oxidized to nitrate compounds by bacteria 
which at first used the ammonia directly as nitrogen food. Such 
a process, though it may have taken place originally, is probably 
not going on at present. 

(2) By Electrical Discharges in the Air. — During the elec- 
trical discharges of thunderstorms there is a continual con- 
version of appreciable amounts of the free nitrogen of the air 
into oxides of nitrogen, which with water yield nitrous or nitric 
acid. 

N + O + electric discharge — > NO 

Nitric oxide 

2 no + o 2 :§: 2 no 2 

3 no 2 + H 2 o :£ 2 HNO3 + no 

Nitric acid 



252 ORGANIC AGRICULTURAL CHEMISTRY 

These reactions are the basis of new and important commercial 
processes for the conversion of atmospheric nitrogen into com- 
pounds useful as soil food for plants. In the Birkelund-Eyde 
process, as carried out in Norway, calcium nitrate is thus made 
and used as a fertilizer. Such fixation of atmospheric nitrogen 
is not only a commercial process, but it is probably a means by 
which soil nitrogen is continually supplied. 

(3) By the Action of Nodule Bacteria. — As just recently 
discussed, bacterial nodules occurring on leguminous plants 
fix atmospheric nitrogen in the plant and indirectly in the soil, 
probably in the form of protein compounds. In the total this 
method is possible of fixing large amounts of free nitrogen and 
is continually going on at present. 

It is possible that in one or perhaps all of these three ways 
atmospheric nitrogen originally entered the soil and became food 
for plants. The last two methods are constantly going on in 
nature under present conditions, tending to preserve nitrogen 
equilibrium. Whatever the original process was, it is true that 
in the soil there is present a large amount of nitrogen in the form 
of nitrate salts, ammonium salts or amino compounds, and this 
nitrogen is the source of all protein nitrogen in plants, except as 
stated in connection with the nodule bacteria. By means of 
this nitrogen, together with the products of photosynthesis, 
the plant is able to metabolize protein compounds which serve 
as its own food supply or as reserve food. This reserve protein 
food, intended for the plant's offspring, becomes, however, 
animal food and in herbivorous animals is the sole source of 
the nitrogen for animal protein. In the metabolic processes 
of animals this plant protein nitrogen, built up into animal 
protein, is again torn down to furnish energy to the animal. 
The nitrogen products of protein katabolism in animals are 
urea and the other -nitrogen compounds of the urine. In the 
form of these compounds in animal manure the original nitrogen 
again reaches the soil. Here they are decomposed by bacterial 
action, yielding ammonia, and this by similar action is converted 
into nitric acid and the cycle of the nitrogen is completed. 



PLANT PHYSIOLOGY 253 

If the animal dies, the unchanged protein of the body de- 
composes bacterially in the soil, yielding simpler compounds, 
amino-acids, etc., and eventually ammonia. This is then 
further changed as above described and the cycle is again 
completed. Thus the nitrogen of animal protein, either as 
dead animal protein or as excretion products of living animals, 
is eventually converted into soil nitrate compounds and as- 
similated by plants as their soil food for the synthesis of new- 
plant protein. 

During the decomposition of organic nitrogen compounds of 
manure or dead animal bodies and the transformation of the 
nitrogen into nitrate compounds, another class of bacteria known 
as denitrifying bacteria cause the loss of some of the nitrogen 
into the atmosphere as free nitrogen. Also some ammonia 
fails to become oxidized and is volatilized as a gas. This 
ammonia gas is absorbed by water and returned to the soil in 
rain. The whole cycle of changes is controlled by conditions of 
equilibrium, both biological and chemical, so that it cannot be 
represented as a clean-cut series of reactions always going in 
one direction. The final results are, however, those which have 
been indicated. 

For the purpose of a review and to condense what has been 
said into a short presentation, we may write the following 
reactions as representing the general course of the cycle of 
changes. 



254 



ORGANIC AGRICULTURAL CHEMISTRY 



Nitrogen Cycle 

by nodule bacteria 
N ^ pi ant p ro tein 



In the atmosphere 



electrically 
N+O >HN0 3 



In the atmosphere 



KNO3 

Nitric acid Nitrates in the soil 



by plants, as soil food 

KNO3 — — : : — r~> Plant protein 

with pnotosyntnesized 
Nitrates of soil carbohydrates 

By animals, as food 
Plant protein > Animal protein 

By animal katabolism 
Animal protein > Urea, etc. 

Utilized by some plants 

In soil, by bacteria 
Urea, etc. and Dead protein > NH3 

In soil 
Utilized by some plants 



In soil, by oxidizing bacteria 
NH3+O < > HN0 5 



Into atmosphere 

and returns to 

soil in rain 

(partial) 



Reducing bacteria .^ 



(partial) 




KNO3 

Nitrates 
In soil 
Repeats 
cycle 



Into atmosphere 
and repeats cycle 



PLANT PHYSIOLOGY 255 

The following diagram also represents the series of changes : 



ATMOSPHERE 
NITROGEN (N) 




SoU plant: food 
NITRIC ACID (HNOo) PLANT 

NITRATES (KNOo) .<*/ PROTEIN 

(Soil) " *#-\fe. 



4? 

[ITR'OGEls 



Oxidizing ^ CYCLE 

. \ <$T J 

AMM (sS{f (NH3> Death and ba/teria ANIMAL PROTEIN 



Animal food 

(metabolism) 

Y 



UREA, etc. jfcT 
OC (OT 2 J 2 



Katabolism 



RESUME 

Plants, like animals, as living organisms, utilize organic food 
consisting of carbohydrates, fats and proteins, for the liberation 
of energy necessary for the life process. In plants, however, 
the net result, or the predominating reaction, is not to expend 
energy but to conserve or store it. The process that produces 
this result is photosynthesis. By the photosynthetic action 
of green plants chlorophyll bodies or chloroplasts, together 
with the green pigment chlorophyll, utilize the kinetic energy 
of sunlight for the synthesis of complex organic compounds 
from the carbon dioxide of the air and water of the air and soil, 
at the same time setting free oxygen which is given off into the 
air. In these complex compounds the used kinetic energy of 
the sun is stored as potential energy. 

The probable direct result of photosynthesis is the carbohy- 
drate glucose. This photosynthesized glucose is converted by 
metabolic changes into more complex carbohydrates, e.g. cane 



256 ORGANIC AGRICULTURAL CHEMISTRY 

sugar, malt sugar, starch, inulin. Carbohydrate material is 
also further metabolized into fat and, with the assistance of 
nitrogen, mostly in the form of nitrates, in the plant's soil food, 
into protein. 

All three of these organic products of photosynthesis and 
metabolism, the carbohydrates, fats and proteins, serve as 
plant cell food for the liberation of energy. They are also 
stored as reserve food supply for the young plant or offspring. 
In addition to this they are converted into building material 
for the plant body, the most abundant substance of this 
kind being cellulose, which forms the cell wall structure and 
which impregnated with resinous compounds results in the 
woody fiber of trees. 

As a net result of all of these reactions, in which chlorophyll 
bodies, chlorophyll and enzymes play an essential part, the 
plant builds up from simple compounds the complex organic 
food constituents which possess the energy of the sun's rays 
stored in potential form. Thus the plant manufactures its 
own energy food which is used either to yield energy or to 
build body substance. Not only, however, does it manufacture 
its own energy food, but in excess of this it stores up a reserve 
supply for its offspring. This reserve supply is often not 
allowed to be used by the young plant, but the plant or some 
part of it is used by animals as food. As animal food both the 
reserve food in seeds, etc., and all of the other constituents of 
the plant body are utilized to a greater or less extent. From 
this food herbivorous animals wholly, and all animals in part, 
obtain the energy necessary for their life process and the ma- 
terial out of which their bodies are built, in this last the in- 
organic foods also taking part. 

References, Section II 

Abderhalden, Lehrbuch der Physiologischen Chemie, 1909. 
Atwater, Principles of Nutrition (U.S. Dept. Agr. Bui. 142), 1902. 
Barthel-Goodwin, Milk and Dairy Chemistry, 1910. 
Bayliss, Nature of Enzymes (Monographs on Bio-Chemistry), 191 1. 



PLANT PHYSIOLOGY 257 

Czapek, Biochemie der Pflanzen, 1913. 

Czapek, Chemical Phenomena in Life, 191 1. 

Euler-Pope, General Chemistry of Enzymes, 191 2. 

Haas & Hill, Chemistry of Plant Products, 1913. 

Hammersten-Mandel, Text-book of Physiological Chemistry, 1901. 

Hawk, Practical Physiological Chemistry, 1914. 

Howell, Text-book of Physiology, 19 10. 

Jordan, Principles of Human Nutrition, 1913. 

Lusk, Elements of the Science of Nutrition, 1909. 

Mathews, Physiological Chemistry, 191 5. 

Pfeffer-Ewart, Physiology of Plants, 1900. 

Salkowski, Practicum der Physiol, and Pathologischen Chemie, 1906. 

Sherman, Chemistry of Food and Nutrition, 191 4. 

Stiles, Nutritional Physiology, 191 2. 



SECTION III 
CROPS. FOODS AND FEEDING 



CHAPTER XV 

OCCURRENCE AND USES OF IMPOR- 
TANT CONSTITUENTS IN AGRICUL- 
TURAL PLANTS 

Having now considered the physiological processes by which 
plants utilize the energy of the sun in synthesizing their own 
food material which is used both to yield energy and to construct 
the body substance, let us now examine different plants as to 
the particular compounds which they contain and the general 
uses to which the plants are adapted. We shall study the 
different constituents according to their occurrence in plants 
which have agricultural importance as crops and the uses to 
which each crop is thus adapted. Generally speaking, plants 
have two main uses economically: (i) as animal food, (2) as 
the basis of important manufactured products. The study in 
detail of their food value to man and animals will be taken 
up in the next chapter. In this chapter we shall consider the 
general distribution and uses of the plant constituents. 

CARBOHYDRATES 

The carbohydrates are the most widely and most abundantly 
distributed of the three groups of organic constituents. There 
is no green plant in which they are not present and in most 
cases they are the predominating constituent. The different 
members of this group that are found in plants may be con- 
sidered in the following order : Polysaccharoses . not sugars — 
cellulose, starch, dextrin, inulin; anhydrides of pentose sugars 
— pentosans; disaccharose sugars — cane sugar, malt sugar; 
hexose monosaccharose sugars — glucose and fructose. 

261 



262 ORGANIC AGRICULTURAL CHEMISTRY 



Cellulose 

Considering all forms of plants and all parts of them, the 
most abundant carbohydrate is cellulose. It is the material 
which is used by the plant for the construction of the cell wall 
and is elaborated as a metabolic product by the cell protoplasm. 

Forms of Cellulose. — In the walls of young cells the cellulose 
is probably pure and is considered simpler in its nature than 
cellulose as usually obtained from fiber plants. 

Three different types or varieties of cellulose are known: 
(a) Normal cellulose as found in the fibers of such plants as 
cotton, flax and hemp; (b) Hemicellulose as found in the 
stems and leaves of green grasses, cereals, etc., and in the cell 
walls of certain seeds, e.g. peas and beans. This is considered 
as simpler than normal cellulose and more like the newly metabo- 
lized cellulose of young cells, (c) Compound cellulose as found in 
the woody cells of ripened grasses and cereals and in trees. 
Also in jute, probably in flax and hemp, and in the cellulose 
fiber of juicy fruits. Each of these different forms of cellulose 
is usually spoken of in the plural, as it is probable that there 
are different individuals or varieties of each. 

Normal Celluloses. — The purest form of cellulose generally 
obtained is the fibrous variety (normal celluloses) as it occurs 
in cotton, flax and hemp. Such cellulose is the most valuable 
of all forms for industrial purposes, and from these sources are 
manufactured all of the various kinds of cloth, thread, string, 
and rope, with the exception of those made of wool and silk. 
From the cotton fiber, as found in the cotton boll, the different 
varieties of cotton cloth, thread and string are made. From 
flax fiber, obtained from the straw of the flax plant, all of the 
like forms of linen are prepared. Hemp fiber, obtained from 
the stalks of the hemp plant, is used in making a stronger kind 
of cloth known as canvas and also string and rope. Jute fiber, 
largely compound celluloses, likewise obtained from the stalks 
of the jute plant, is made into canvas, sacking and carpets. 
Cellulose, mostly as cotton, is also used in making exceedingly 



PLANT CONSTITUENTS — CARBOHYDRATES 263 

important chemical derivatives such as cellulose explosives, 
collodion, celluloid, mercerized cotton and artificial silk. The 
chemical nature of these derivatives has been discussed in 
Section I (p. 127). 

Cellulose in the form of flax fiber or old linen cloth is also 
used to make the best grades of paper. Cotton fiber or cotton 
cloth are used for poorer grades of paper, and a large amount 
of paper used, especially for newspapers, is made from wood 
cellulose. 

As an agricultural crop cotton is grown most abundantly in 
the United States, but also to a greater or less extent in South 
America, India, Egypt and Australia. The chief production 
of flax and hemp is in Russia. Jute comes mostly from India, 
where its cultivation is replacing that of indigo, which is now 
made largely by synthetic processes. Considerable flax and 
some jute come from the United States. 

Analysis of cotton fiber by Bowman, as cited by Haas and 
Hill, shows it to have the following composition : 

Cellulose 91.00 per cent 

Wax, Oil, Fat 35 per cent 

Protoplasm 53 per cent 

Mineral Matter 12 per cent 

Water 8.00 per cent 

Konig's investigations l give the following amounts of pure 
cellulose in some plants : 

Cotton 88.3 per cent 

Flax and Hemp 72-73 per cent 

Jute 54 per cent 

Beech and Oak Wood . . . 35-38 per cent 

Hemicelluloses. — In the young plant cell, as previously 
stated, the wall is probably pure cellulose. Such cellulose 
would be more easily soluble than the normal cellulose, and 

^uhn, "Chemie der Zellmembran" ; Z. Nahr. Genuss., XXVII, 21 (1914). 



264 ORGANIC AGRICULTURAL CHEMISTRY 

would also hydrolyze with comparative ease, yielding mono- 
saccharose products. The cellulose which is present in peas, 
beans, etc., and in green grasses seems to be a simpler and purer 
cellulose than the normal fibrous variety, and does in fact dis- 
solve more easily and hydrolyze more easily than the normal. 
This form has been termed hemicelMose. Other substances 
known as mannans, galactans and pentosans (pp. 270, 272) are 
either identical with hemicelluloses themselves or are contained 
in them. 

Lignocelluloses. — As the cell walls, especially of the stems, 
stalks and trunks of plants, become older they take on a special 
character which is known as woody. They then possess much 
greater hardness and strength and form the supporting struc- 
ture of plants. The change in character is due to a change in 
chemical composition resulting from the infiltration into the 
original cell wall of noncellulose substances possessing a gummy 
or resinous nature. These substances are known in general as 
lignins, and the celluloses formed are called ligno-celluloses. 
It is probable that these lignins are in actual chemical combina- 
tion with the cellulose, though it may be that they are simply 
mixed with it. The exact chemical nature of the lignins is 
also unknown, but they are undoubtedly of pentosan character. 
They yield pentose sugars on hydrolysis. While the normal 
celluloses are the chief source for the manufacture of the best 
grades of paper, the lignocelluloses of the softer woods, such 
as spruce, fir, etc., are being used almost exclusively in the 
manufacture of paper for newspapers and similar uses. In 
making the paper from wood more or less of the lignins are 
removed. Cellulose so obtained amounts to about 55 per cent 
of the weight of the wood itself. (See also Paper, p. 126.) 

Pectocelluloses. Pectins. — Two other kinds of compound 
celluloses should be mentioned. The first of these is the pecto- 
celluloses, in which cellulose has associated with it noncellulose 
substances termed pectins analogous to the lignins of the ligno- 
celluloses. These pectins, like the lignins, are probably not 
simple substances, but are of carbohydrate character, perhaps 



PLANT CONSTITUENTS — CARBOHYDRATES 265 

polysaccharoses like pentosans. They are soluble in water 
and on boiling the solution, or by the addition of alcohol, they 
gelatinize. It is these pectins which are present in the juices 
of succulent fruits, and which on the concentration of the juice 
by boiling produce a jelly. The other variety of compound 
celluloses is that found in the corky tissue of plants, and is 
termed adipo-cellulose. The noncellulose constituent is prob- 
ably of fatty nature, and is known as cutin. In all plants 
containing largely hemicelluloses or compound celluloses, the 
normal cellulose is also present to a greater or less extent. 

Cellulose as Food. — As a constituent of human foods cellulose 
does not play an important part and is very slightly digested. 
In the case of herbivorous animals, like the cow, sheep and 
horse, however, they constitute a large part of their normal 
food, and are thus of far greater importance than with man. 
The most easily digested form of cellulose is that of the hemi- 
celluloses, which, however, are not as abundant as the normal 
celluloses, which probably rank next in order of digestibility. 
The least digestible form is that of the lignocelluloses and of 
these those found in hay and straw are the most valuable. In 
the digestion of cellulose by herbivorous animals an amount 
varying from 30 to 60 per cent is considered as digestible. 
Of this amount, however, a considerable portion is fermented 
by bacteria in the intestines, and is converted into products, 
such as methane gas, which are unabsorbed. This necessitates 
a correction for the digestibility of cellulose constituents in 
order to determine the amount actually utilized by the animal. 
This will be considered again (p. 297). The cellulose actually 
utilized by animals is considered to have the same food value 
as the other carbohydrates, such as starch and sugar. 

Crude Fiber. — In the analysis of cellulose-containing foods 
the substance is usually determined in the form of what is 
commonly termed crude fiber. If such a food is boiled with a 
1.25 per cent acid solution and then filtered, and the undissolved 
residue again boiled with a 1.25 per cent alkali solution, the 
undissolved residue finally obtained is largely cellulose, and is 



266 



ORGANIC AGRICULTURAL CHEMISTRY 



TABLE VI 

Cellulose Content of Crops 
Crude Fiber 



Crop 


(Fresh 
Basis) 


(Dry Basis) 




Cotton fiber 


91.0 


99.0 


Bowman (Haas & Hill, p. 129) 1 


Pine wood 




50-60 






Wheat straw .... 




38.1 


42.1 


J. & W., pp. 12-19 2 


Oat straw 




37-0 


40.7 


J. & W., pp. 12-19 


Corn stalks (cured) . . 




11.0 


34-8 


J. & W., pp. 12-19 


Corn stover (cured) 




19.7 


33-o 


J. & W., pp. 12-19 


Corn fodder (cured) 




14-3 


24.7 


J. & W., pp. 12-19 


Timothy grass . . 




11.8 


30.7 


J. & W., pp. 12-19 


Timothy hay . . 






29.0 


33-5 


J. & W., pp. 12-19 


Red clover grass 






8.1 


27.8 


J. & W., pp. 12-19 


Red clover hay 






24.8 


29.1 


J. & W., pp. 12-19 


Alfalfa grass . 






7-4 


26.2 


J. & W., pp. 12-19 


Alfalfa hay 






25.0 


27-3 


J. & W., pp. 12-19 


Cowpea (hay) . 






20.1 


22.5 


J. & W., pp. 12-19 


Cowpea (peas only) 




4.1 


4.8 


J. & W., pp. 12-19 


Soja bean (bean only) 




4.8 


5-4 


J. & W., pp. 12-19 


Sugar cane .... 




7.0 


28.0 


Konig, p. 896 » 


Oats .... 






9.5 (11.24) 


10.8 (12.20) 


J. & W., pp. 12-19 (Bui. 120, p. 34) 4 


Wheat (spring) 






1.8 (2.39) 


2.0 (2.66) 


J. & W., pp. 12-19 (Bui. 120, p. 33) 


Wheat (winter) 






1.8 (2.23) 


2.0 (2.49) 


J. & W., pp. 12-19 (Bui. 120, p. 33) 


Barley . . . 






2.7 (S-u) 


3-o (5-64) 


J. & W., pp. 12-19 (Bui. 120, p. 36) 


Rye . . . 


. 




1.7 (2.08) 


1.9 (2.30) 


J. & W., pp. 12-19 (Bui. 120, p. 35) 


Sorghum grain 






2.6 (1.58) 


3.0 (1.80) 


J. & W., pp. 12-19 (Bui. 120, p. 41) 


Maize (flint) . 






i-7 


i-9 


J. & W., pp. 12-19 


Rice .... 






0.2 


0.2 


J. & W., pp. 12-19 


Wheat middlings 




4-6 (6.3) 


5-2 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 50 5 ) 


Wheat bran . . . 




9-o (9-5) 


10.2 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 51) 


Malt sprouts . . . 




10.7 (12.5) 


11.8 


J. & W., pp. 12-19 (Mass. Exp. 








Sta., p. 49) 


Linseed meal (new process 


9-5 (8.6) 


10.5 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 47) 


Linseed meal (old process) 


8.9 (8.9) 


9-7 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 46) 


Cottonseed meal . . . . 


5-6 (9.4) 


6.1 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 46) 


Germ meal (maize) . . . 


4.1 


4.6 


J. & W., pp. 12-19 


Gluten meal 


1.6 (2.3) 


1.8 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 47) 


Cassava root 


1.1 


3-7 


Konig, p. 1495 


Turnips 


1.2 


12.2 


J. & W., pp. 12-19 


Mangels 


0.9 


9-5 


J. & W., pp. 12-19 


Rutabaga 


1.3 


11.0 


J. & W., pp. 12-19 


Cabbage 


IS 


15-5 


J. & W., pp. 12-19 


Red beets 


0.9 


7-8 


J. & W., pp. 12-19 


Sugar beets 


0.9 


6.5 


J. & W., pp. 12-19 


Potatoes 


0.6 
1-3 


2.7 

3-6 


J. & W., pp. 12-19 


Sweet potatoes . . . . 


J. & W., pp. 12-19 



1 Haas & Hill, I.e. (Table V). 2 J. & W., I.e. (Table V). 

s Konig, I.e. (Table V). * Bui. 120, I.e. (Table V). 

6 "Mass. Exp. Sta."; Smith & Beals, Com'l. Feeding Stuffs, Mass. Agr. Exp. 
Sta. Bui. No. 1, 1914. 



PLANT CONSTITUENTS — CARBOHYDRATES 267 

called crude fiber. As there is always some mineral matter 
present the actual determination is made by drying the cellulose 
as above obtained and igniting it. The loss of dry material 
on ignition is calculated as the actual crude fiber. (See below.) 
As the method is wholly an empirical one, the crude fiber does 
not represent pure cellulose, but is an approximation to it. 
Probably the greater part of the crude fiber represents normal 
celluloses, but with more or less unhydrolyzed hemi- and ligno- 
celluloses. Part of these latter are, however, dissolved by the 
treatment with acid and alkali. 

Cellulose Content of Crops. — The preceding table gives the 
amounts of cellulose determined as crude fiber which are pres- 
ent in the more important crops. 

EXPERIMENT STUDY XXXIII 
Cellulose in Plants 

Cotton. Examine cotton fiber and recall the study in Experiment 
XXV. This is practically pure cellulose. (See analysis of cotton, 
p. 263.) 

Crude Cellulose. Crude Fiber. Use 2.0 g. of ground hay or 
grass. Place in a 500 c.c. flask and add 200 c.c. of 1.25 per cent hydro- 
chloric acid, and boil with return condenser for one half hour. Filter 
through a linen filter. Wash with hot water. Return the residue 
to the flask and add 200 c.c. 1.25 per cent sodium hydroxide and boil 
again with return condenser for one half hour. Filter through asbestos 
and wash as before. The residue consists of the ash constituents plus 
the crude cellulose. After drying, the loss of weight on ignition rep- 
resents the crude cellulose, or, as it is termed, crude fiber. 

Starch 

The next carbohydrate to be considered is starch, with which 
we may also group dextrin and inulin. While starch does not 
occur as abundantly in plants as a whole as does cellulose, yet 
it far outranks it in importance and value as a food. In fact, 
starch is the most important carbohydrate food for both man 
and animals. 



268 ORGANIC AGRICULTURAL CHEMISTRY 

Starch as Food. — Physiologically starch is a reserve food 
material for the plant itself, as has already been discussed. 
It occurs in the leaves and other green parts of all green plants, 
where, as we have shown, it is a temporary reserve material, 
being immediately converted into sugars and translocated. 
In these parts of the plant it possesses food value for animals, 
but as it never collects in any amount, its actual value is 
slight, the chief carbohydrate constituent here being cellulose. 

Those portions of the plant in which starch is most abundant 
are the strictly reserve organs, e.g. seeds, tubers, roots, etc. 
In these organs the plant has stored large amounts of starch, 
for the use of its offspring or for renewed growth, and it is these 
storage houses of the plant which form the most valuable animal 
foods. The three most important groups of plants in this respect 
are : (i) cereal plants, in which the starch is stored in the seed, 
i.e. the cereal grains, e.g. wheat, maize, oats, barley, rye, sorghum 
grain, millet, etc. ; (2) tuber-forming plants, e.g. potato ; (3) roots 
of certain plants, e.g. arrowroot, cassava, etc. ; (4) unripe fruits, 
e.g. apples, pears, etc., which are not, however, important as a 
source of starch because the fruit is never used in this state, 
and on ripening the starch is converted into sugars. 

As was stated in the chapter on the chemistry of carbo- 
hydrates, the grains of starch found in different plants have in 
each case a distinctive microscopical structure. As a food 
material there is no difference in these various forms, so that in 
this respect starch is a single substance. Both human beings 
and animals digest starch ; in the former case it is easily digested 
only when first cooked, but in the latter raw starch is the 
common form in which the food is eaten. Its common and 
abundant occurrence in so many foods makes it in many in- 
stances the particular constituent upon which the food value 
of the material largely depends. Several forms of pure starch 
are used as human food, e.g. ordinary cooking starch, usually 
obtained from corn, and tapioca, which is a specially prepared 
form of starch obtained from the cassava plant. 

Industrial Uses. — For industrial purposes, such as the manu- 



PLANT CONSTITUENTS — CARBOHYDRATES 



269 



TABLE VII 

Starch Content of Crops 

Nitrogen-free Extract 

(starch, sugars, pentosans) 



Crop 



(Fresh Basis) 



(Dry Basis) 



Cassava root . 
Maize (Flint) . 
Maize (sweet) 
Wheat (spring) 



Wheat (winter) .... 

Sorghum (grain) .... 

Barley 

Rye 

Oats 

Wheat middlings . . . 

Wheat bran 

Malt sprouts 

Rice 

Gluten meal 

Germ meal 

Cottonseed meal .... 
Linseed meal (new process) 
Linseed meal (old process) 
Soja bean . . 
Cowpeas . . 
Potatoes . . 
Sweet potatoes 
Red beets . . 
Sugar beets . 
Turnips . . . 
Carrots . . . 
Mangels . . 
Rutabaga . . 
Onions . . . 
Cabbage . . 
Cowpeas (fresh) 
Cowpeas (hay) 
Maize fodder (cured) 
Maize stover (cured) 
Maize stalks (cured) 
Timothy grass 
Timothy hay . 
Red clover, grass, 
Red clover hay 
Alfalfa, grass . 
Alfalfa hay 



26.5 

70.1 

67.0 

71.2 (70.4) 

72.0 (73-55) 

70.0 (72.03) 

69.8 (68.96) 

72.5 (72.71) 

S9-7 (61.10) 

60.4 
53-9 
48.5 
79.2 
52.4 
64.0 
23.6 
38.4 
35-4 
28.8 
55-7 
17-3 
24.7 

8.0 

9-8 

6.2 

7-6 

5-5 

7-5 

9-4 

3-9 

7-1 
42.2 
34-7 
31-9 
17.0 
20.2 
45 -o 
13-5 
38.1 
12.3 
42.7 



89.0 

79.0 

73-4 

79-5 (78.16) 

80.6 (81.77) 

80.1 (81.58) 
78.4 (76.05) 

82.2 (80.24) 

67.0 (66.29) 

68.7 
61.3 
54-2 
9o.5 
S7-9 
71.7 
25.8 
42.8 
39-2 
32.2 
65.S 
82.2 
86.3 
68.4 
73-3 
64.9 
66.3 
62.0 
66.8 
76.5 
40.7 
43-6 
47.2 
60.1 
53-2 
54-1 
52.8 
51.7 
45-8 
45-2 
43-9 
46.6 



12-19 (Bui. 120, 

12-19 (Bui. 120, 

12-19 (Bui. 120, 

12-19 (Bui. 120, 



Konig, p. 1495 1 

J. &;W., pp. 12-192 

J. & W., pp. 12-19 

J. & W., pp. 12-19 (Bui. 120, 

P- 34) 3 
J. & W., pp. 

P- 34) 
J. & W., pp. 

p. 42) 
J. & W., pp. 

P- 40) 
J. & W., pp. 

P- 35) 
J. & W., pp. 12-19 (Bui. 120, 

p. 24) 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 



* Konig, l.c. (Table V). 2 J. & W., l.c. (Table V). 3 Bui. 120, l.c. (Table V). 



270 ORGANIC AGRICULTURAL CHEMISTRY 

facture of glucose, which is really a food use, and as laundry 
starch, or as sizing for cloth or paper, it is generally obtained 
from either corn or potatoes, which are the two most common 
and abundant sources. 

Starch Content of Crops. — The preceding table gives the 
percentage amounts of starch (in some cases including small 
amounts of sugars) in some of the more important crops. The 
figures are those for " nitrogen free extract," which ordinarily 
includes with the starch the small amounts of sugars and pen- 
tosans if these have not been separately determined. 

EXPERIMENT STUDY XXXIV 

Starch 

(i) Cut a wheat grain and moisten the cut surface with iodine solu- 
tion. Note test for starch. Repeat with other cereal grains. 

(2) Cut a slice of potato and moisten similarly with iodine solution. 

(3) Cut a slice of a green apple and similarly test for starch by 
moistening the entire surface. Repeat the test with a slice of a ripe 
apple. Note difference in amount and location of starch. 

(4) Wash out the starch from some wheat flour made into a dough 
and kneaded in the hand under a small stream of running water. 
Keep the dough in a compact ball and continue to knead until prac- 
tically all starch is washed out and an elastic gummy ball is left. 
This is gluten. Test for protein (Experiment XVIII). Collect the 
starchy washings and allow to settle. Examine the starch residue. 

(5) Peel a potato and grate it into a large dish of water. Allow 
the starch to settle and examine it. This is the principle of the prepa- 
ration of commercial potato starch. 

Dextrin, Inulin, Mannan, Galactan 

While there is only one form of starch chemically considered, 
there are several other substances occurring in plants which 
are isomeric with it and which are often included with it in a 
general group sometimes termed the starches. They all have 
the same composition formula, viz. (C 6 Hi O 5 )^. They differ 
probably in complexity of the molecule, but their chief differ- 



PLANT CONSTITUENTS — CARBOHYDRATES 2 7 1 

ence is in the hexose monosaccharoses which they yield on 
hydrolysis. Starch and dextrin each yield glucose or dextrose 
and are, therefore, both termed dextrosans or glucosans. 
Inulin, on the other hand, yields levulose and is termed a 
levulosan. Similarly, the mannans or mannosans are starch- 
like polysaccharoses which yield mannose and the galactosans 
or galactans yield galactose. 

Dextrin. — The most important member of the group is 
dextrin. It occurs in quantity only in a few plants, for it is a 
transitory substance in the enzymatic hydrolysis of starch by 
diastase. In the chapter on salivary digestion (Chapter XI), 
the formation of dextrin in its several forms as an intermediate 
substance in the hydrolysis of starch to maltose sugar by 
ptyalin has been fully discussed. It differs from starch in 
being soluble in cold water. As a food substance it has the 
same value as starch. 

It may be prepared by the action of enzymes on starch or 
by heating starch to 23o°-26o° C. In this latter way it is 
made for industrial use. We spoke of the use of starch as a 
sizing material for cloth and paper. Strictly speaking, except 
in laundering, it is not starch, but dextrin, made as above, 
which is generally used in this way. It is also used as an ad- 
hesive gum or mucilage. 

Glycogen. — This compound may be referred to in this con- 
nection, for it is also a glucosan. It does not occur in green 
plants, but is found in some fungi, especially yeast, and in 
some other cryptogamous plants. It is known as animal starch 
and has been discussed in connection with the metabolism of 
carbohydrates in animals (Chapter XII). 

Inulin. — This isomer of starch differs from it and from 
dextrin in yielding only levulose on hydrolysis. Like starch it 
is a reserve food in certain plants, especially the dahlia, where 
it occurs in the tubers. It is also present in the artichoke 
and in cherry roots. It is not hydrolyzed by diastase or ptyalin 
and is, therefore, undigested by animals. The enzyme which 
hydrolyzes it is known as inulase. 



272 ORGANIC AGRICULTURAL CHEMISTRY 

Mannan and Galactan. — These two starch-like poly- 
saccharoses are similar substances and are associated with 
cellulose in the form of hemicelluloses already discussed. 
They are found in wheat and in numerous other seeds, especially 
legumes, but not in amounts sufficient to deserve more atten- 
tion. A particular source of mannan is the substance known 
as vegetable ivory. Agar-agar is a galactan. On hydrolysis 
mannan yields mannose, and galactan, galactose. 

Pentosans 

The polysaccharoses which we have just considered are all 
hexosans, i.e. they yield hexose sugars on hydrolysis. Analo- 
gous to these we have polysaccharoses which on hydrolysis 
yield pentose sugars (arabinose, xylose, etc.). They are termed 
pentosans. They have already been referred to as constituting 
the noncellulose part of lignocelluloses and probably also 
pectocelluloses. They constitute the gummy or resinous 
material which on hardening within the cell wall produces the 
lignocelluloses of woody fibers in trees and the stems of cereals 
and grasses. 

They are found in purer form in what are known as natural 
gums, such as gum Arabic, gum tragacanth, wood gum, etc. 
These natural gums are not simple pentosan polysaccharoses, 
but are of a complex glucoside nature which readily yield first 
the pentosan and then the pentose sugar on hydrolysis. Some 
gums also yield galactans and galactose. They are also con- 
sidered as acid compounds which are present in the gums as 
salts of potassium, calcium or magnesium. 

Whether, however, they are present as constituents of lig- 
nocelluloses, pectocelluloses or natural gums, the pentosans 
yield pentose sugars on hydrolysis and probably possess a 
food value close to that of other polysaccharoses. Their wide 
distribution in plants gives them an importance as food con- 
stituents, and their determination is a usual part of food analysis, 
especially in connection with ordinary farm crops used as food 
for domestic animals. The principle of the analysis is that 



PLANT CONSTITUENTS — CARBOHYDRATES 273 

on hydrolysis with boiling acid the pentose sugar is obtained 
and the pentose sugar on boiling with acid (hydrochloric) is 
converted into furfural. The furfural forms an insoluble com- 
pound with phloroglucinol, which is weighed and the pentose 
and pentosan calculated from this. 



EXPERIMENT STUDY XXXV 
Determination of Pentosans 1 

Place 5.0 g. of finely ground wheat or oat straw in a flask, together 
with 100 c.c. of 12 per cent hydrochloric acid (specific gravity, 1.06), 
and several pieces of recently heated pumice stone. Place the flask 
on a wire gauze, connect with a condenser, and heat, rather gently at 
first, and so regulate as to distill over 30 c.c. in about ten minutes, the 
distillate passing through a small filter paper. Replace the 30 c.c. 
driven over by a like quantity of the dilute acid added by means of a 
separatory funnel in such a manner as to wash down the particles 
adhering to the sides of the flask, and continue the process until the 
distillate amounts to 360 c.c. To the completed distillate gradually 
add a quantity of phloroglucinol (purified if necessary) dissolved in 
12 per cent hydrochloric acid and thoroughly stir the resulting mix- 
ture. The amount of phloroglucinol used should be about double 
that of the furfural expected. The solution first turns yellow, then 
green, and very soon an amorphous greenish precipitate appears, 
which grows rapidly darker, till it finally becomes almost black. 
Make the solution up to 400 c.c. with 12 per cent hydrochloric acid, 
and allow to stand overnight. 

Filter the amorphous black precipitate through an asbestos felt 
in a tared Gooch crucible, wash carefully with 150 c.c. of water in 
such a way that the water is not entirely removed from the crucible 
until the very last, then dry for four hours at the temperature of 
boiling water, cool and weigh, in a weighing bottle, the increase in 
weight being reckoned as phloroglucid. To calculate the furfural, 
pentose, or pentosan from the phloroglucid, use the following formulas 
given by Krober : 

1 Official Methods of Analysis, A. O. A. C, U. S. Dept. Agr. Bur. Chem. Bui. 107, 
p. 54 (1912). 
T 



274 ORGANIC AGRICULTURAL CHEMISTRY 

(a) For weight of phloroglucid " a " under 0.03 gram. 

Furfural = (a + 0.0052) X 0.5170 
Pentoses = (a + 0.0052) X 1.0170 
Pentosans = (a + 0.0052) X 0.8949 

(b) For weight of phloroglucid " a " over 0.300 gram. 

Furfural = (a + 0.0052) X 0.5180 
Pentoses = (a + 0.0052) X 1.00.26 
Pentosans = (a + 0.0052) X 0.8824 

For weight of phloroglucid " a " from 0.03 to 0.300 grams use 
Krober's table x or the following formulas : 2 

Furfural = (a + 0.0052) X 0.5185 
Pentoses = (a +0.0052) X 1.0075 
Pentosans = (a + 0.0052) X 0.8866 

Sugars 

Both monosaccharoses and disaccharoses are found very 
widely distributed in the vegetable kingdom. They are all 
soluble compounds and are, therefore, found in the plant juices, 
especially in fruits. 

Sucrose. — Of the three common disaccharose sugars, viz. 
sucrose or cane sugar, maltose or malt sugar and lactose or milk 
sugar, the first two are present in plants, while the last is found 
only in animals. 

The most abundant disaccharose in plants is common cane 
sugar, or sucrose. Its most important sources are the juice of 
the sugar cane and of the sugar beet. From these two agri- 
cultural crops almost all of the sugar used as human food is 
obtained. This has all been fully discussed in the chapter on 
the chemistry of the carbohydrates (Chapter VII). Numerous 
other plants contain cane sugar in considerable quantity, but, 
with the exception of the sorghum cane and the sap of the hard 
or sugar maple, none of them serve as commercial sources of 
sugar. 

1 J. Landw. 48, 379, 1900. See p. 226 of the above bulletin. 

2 These factors were calculated from Krober's tables by C. A. Browne. 



PLANT CONSTITUENTS — CARBOHYDRATES 275 

Whether cane sugar is originally formed in the plant from 
the monosaccharoses, glucose and fructose, is uncertain. From 
its wide distribution in plant juices it seems probable that it is a 
translocation form of carbohydrate from which the glucose 
and fructose in fruits are formed. 

In all plants where cane sugar is present it is an important 
food material possessing approximately the same value as 
starch. Because of its abundance in sugar cane and sugar 
beet it is one of the most valuable of the carbohydrates found 
in agricultural crops. The amount present in some of the 
common crops will be seen from the table given later. 

Maltose. — This disaccharose is a transition substance in 
the conversion, by diastase, of reserve starch into glucose and is 
found chiefly in sprouting grain or malt. It has also been 
found in the sap of green leaves. As it is simply transition 
material in plants it plays no large part in crops as a food sub- 
stance. In malted grain produced artificially for the manu- 
facture of alcohol by fermentation it is present in large amount. 
The waste mash from distilleries contains some unchanged 
maltose and glucose and is valuable as an animal food. In 
preparing some human cereal foods the grain is sometimes 
malted and in these maltose sugar is present. 

Monosaccharoses. — The only two monosaccharoses that 
are present as such in plants are the two hexoses glucose and 
fructose. These two sugars occur in the leaf sap and, as has 
been stated, glucose is probably the first photosynthesized carbo- 
hydrate. Except in their physiological relations, the most 
important occurrence of glucose and fructose is not in the leaves 
but in the juice of fruits. In most fruit juices the two sugars 
occur together, from which fact we derive their common names 
of grape sugar and fruit sugar. In these juices they have 
probably been produced by the hydrolysis of cane sugar, which 
is undoubtedly their precursor. In almost all plant juices and 
in seeds some glucose and fructose are usually found. When 
present in plants, their food value is practically that of starch 
and the other sugars. 



276 



ORGANIC AGRICULTURAL CHEMISTRY 



The monosaccharoses mannose and galactose do not occur 
free in plants, but are derived by hydrolysis from the starch- 
like poly saccharoses mannan and galactan just considered. 
The same is true of the pentose monosaccharoses arabinose 
and xylose obtained from the pentosans. 

Sugar Content of Crops. — The sugar content of crops is 
given in the following table : 

TABLE VIII 

Sugar Content of Crops 
(Fresh Basis) 



Crop 


Sucrose 


Invert Sugar 


Pectins 


Organic 
Acids 




Sugar cane . . 


i4-3 (1S-20) 


8.6 
other carbo- 
hydrates 






Konig, pp. 896, 1 507 * 


Sugar beet . . 


12.3-17.4 


2.9 
other carbo- 
hydrates 






Konig, p. 761 


Sorghum cane 


7.0-12.0 










Maple sap . . 


2.0-3.0 










Red beet . . 


0.5 








Konig, p. 777 


Carrot . . . 


6.4 








Konig, p. 765 


Sweet potato . 


2.3 








Konig, p. 1495 


Onion . . . 


5-8 








Konig, p. 780 


Cabbage . . 


i-9 








Konig, p. 790 


Wheat . . . 


0.3 


•03 


.16 Dextrin 




Bui. 13, p. 1207 2 


Barley . . . 


0.2 


.02 


.14 Dextrin 




Bui. 13, p. 1207 


Rye .... 


0.4 


.07 


.22 Dextrin 




Bui. 13, p. 1207 


Oats .... 


0.2 


•03 


.26 Dextrin 




Bui. 13, p. 1207 


Apple . . . 


0.9-6.0 


5.0-14-1 


3-2 


0.7-1.5 


Konig, pp. 820, 854 


Grape . . . 




(14-4) 
(total sugar) 


1.1 


0.7 


Konig, p. 842 


Peach . . . 


5-6 


3-6 


0.5 


0.7 


Konig, p. 829 


Strawberry 


1.1 


5-i 




1.1 


Konig, p. 840 


Orange . . . 


2.9 


2.8 




1.4 


Konig, p. 849 


Lemon . . . 




(0.4) 

(total sugar) 




5-4 


Konig, p. 849 



1 Konig, I.e. (Table V). 

2 "Bui. 13," U. S. Dept. Agr. Bur. Chem. Bui. 13, part ix (1898). 



CHAPTER XVI 

OCCURRENCE AND USES OF IMPORTANT 
CONSTITUENTS IN AGRICULTURAL 
PLANTS {Continued) 

FATS AND WAXES 

Plant Fats as Food. — In those crops used as food for domestic 
animals fats do not play so important a part as do either car- 
bohydrates or proteins. They are present in much smaller 
amounts, in general, and in the case of herbivorous animals 
they contribute only a small amount to the total energy value 
of the food. It will be recalled also that body fat in animals 
is formed largely from carbohydrate and not from fat food. 
While this is true of most domestic animals, it is not true of 
human beings. Some of the plants or plant parts used by 
man as food contain large amounts of fat or oil, and from such 
sources a considerable part of the total energy of the body is 
derived. 

Occurrence. — Fats, mostly as oils, occur usually as a re- 
serve food in seeds, often largely replacing carbohydrates. They 
are also found, to some extent, but never in large amounts, 
in the vegetative organs, as in grasses, etc. 

In seeds, which contain mostly starch, as the cereal grains, 
the fat is stored immediately around the germ so that when the 
germ is removed most of the fat goes with it. This is the 
reason for the high fat content of so-called germ meal. In 
seeds which are very rich in fat, as in the castor oil bean, cotton- 
seed, flaxseed, olive, brazil nut, etc., the fat is variously distrib- 
uted throughout the seed. 

In the case of common crops, whether these are seeds, as the 

277 



278 ORGANIC AGRICULTURAL CHEMISTRY 

cereal grains, or vegetative parts, as the grasses, etc., there is 
usually no distinction made between fats and waxes, as both 
are in small amount, the value of the plant depending upon its 
food value as a whole. In other cases plants are valuable 
because of a certain fat- or wax-bearing part, as in the castor 
oil bean, or they may have a double value, one part serving as 
food or for industrial uses, while another part yields an oil 
which may also be used either as food or industrially, as in the 
case of the flaxseed and cottonseed. 

Oil-yielding Plants. — The most important oil-producing 
plants are as follows : 

Olive. — This is grown largely for the oil, which is expressed 
from the flesh of the fruit, the oil being then used as a food or 
for making soap. Some oil is also obtained from the kernel. 
The fruit itself is used directly as a food. 

Cottonseed. — The cottonseed is a by-product from the 
cotton boll after the removal of the fiber. The oil is expressed 
from the seed and is used as food either directly as a substitute 
for olive oil or indirectly as a culinary article. After the oil is 
extracted from the seed the ground residue is known as cotton- 
seed meal. It still contains considerable oil and also protein, 
and is largely used as a stock food. 

Peanut. — The oil is obtained from the seed and is used as 
food. The seed itself is used as food either directly or in the 
form of peanut butter. 

Sesame. — The seed of this plant and the oil obtained from 
it are both used as food, mostly in India. The extracted residue 
is used as a stock food similar to cottonseed meal. 

Castor Bean. — This plant is grown wholly for the oil which 
is obtained from the seed. The oil is used both medicinally 
and as a lubricant. The extracted residue cannot be used as a 
stock food, but is used as a fertilizer and is called castor pomace. 

Palm. — Both the fleshy part of the palm fruit and also the 
kernel are used for securing an oil used largely in making soap. 
The oils are called palm oil and palm nut oil and are solid at 
ordinary temperatures. 



PLANT CONSTITUENTS— FATS, PROTEINS 



279 



TABLE IX 

Fat Content of Crops 
Ether Extract 



Crop 



Olive, pulp 

Olive seed (without shell) 
Castor oil bean . . . . 

Cacao bean 

Palm nut 

Cocoanut 

Brazil nut 

Peanut 

English walnut (dry) . . 

Sesame seed 

Sesame seed (cake) . . . 

Cottonseed 

Cottonseed meal . . . . 



Flaxseed 

Linseed meal (new process) 



Linseed meal (old process) 



Germ meal (maize) 
Maize (flint) . 
Maize (sweet) 
Wheat (spring) 
Wheat (winter) 
Sorghum grain 
Barley . . . 
Rye .... 
Oats .... 
Rice .... 
Wheat middlings 



Wheat bran . 

Malt sprouts . 

Wheat straw . 
Oat straw . . 
Timothy grass 
Timothy hay . 
Red clover, grass 
Red clover hay 
Alfalfa, grass . 
Alfalfa hay 
Cowpeas (cured) 
Cowpeas (peas) 
Soja bean . . 
Maize fodder (cured) 
Maize stover (cured) 
Maize stalks (cured) 



(Fresh 
Basis) 



56-4 
12.3 
Si-4 
44.4 
48.7 
67.0 
67.7 
44-5 
S8.S 
45-6 
10-15 
19.1 
I3-I (7-6) 

34-4 
3.o (3-8) 

7.9 (7.0) 

7-4 
5-o 
7.6 
2.2 (2.23) 
2.1 (1.71) 

3.6 (2.86) 
1.8 (1.69) 

1.7 (1.66) 
5.o (3.99) 

0.4 
4-o (S-3) 

4.0 (4.9) 
1-7 (1.3) 

1-3 

2.3 
1.2 

2-S 
I.I 

3-3 
1.0 
2.2 
2.9 
1.4 
16.9 
1.6 
1.1 
o.S 



(Dry Basis) 



74-4 
I3-I 
55-3 
47-4 
53-2 
71. 1 
71.8 
48.1 
63.0 
48.3 

22.0 

14.2 

37-8 
3-3 



8.3 
5-6 
8.3 
2.5 (2.48) 
2.3 (1.91) 
4-1 (3-25) 
2.0 (1.87) 
1.9 (1.83) 
5-6 (4-33) 
0.4 
4-5 

4-5 
1.9 

1.4 
2-5 
31 
2.9 
3-9 
3-9 
3-4 
2.4 
3-2 
1-7 
18.9 
2.8 
1-7 
1.6 



Molinari, p. 391 1 

Molinari, p. 391 

Konig, p. 613 2 

Konig, p. 1022 

Konig, p. 614 

Konig, p. 616 

Konig, p. 616 

Konig, p. 615 

Konig, p. 611 

Konig, p. 613 

Molinari, p. 591 

Konig, p. 615 

J. & W., pp. 12-19 s (Mass. Exp. 
Sta. p. 46) * 

Konig, p. 606 

J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 47) 

J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 47) 

J. & W., pp. 12-19 

J. & W., pp. 12-19 

J. & W., pp. 12-19 

J. & W., pp. 12-19 (Bui. 120, p. 33) 5 

J. & W., pp. 12-19 (Bui. 120, p. 33) 
pp. 12-19 (Bui. 120, p. 42) 
pp. 12-19 (Bui. 120, p. 36) 
pp. 12-19 (Bui. 120, p. 35) 
pp. 12-19 (Bui. 120, p. 24) 
pp. 12-19 

pp. 12-19 (Mass 



J. & W., 
J. & W. 
J. & W., 
J. & W., 
J. & W., 
J. & W. . 

Sta., p. 50) 
J. & W., pp. 
Sta., p. 51) 
J. & W., pp. 
Sta., p. 49) 
J. & W., pp. 12-19 
pp. 12-19 
pp. 12-19 
pp. 12-19 
pp. 12-19 
pp. 12-19 
, pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 
J. & W., pp. 12-19 



12-19 (Mass. 
12-19 (Mass. 



Exp. 
Exp. 
Exp. 



J. &W 
J. &W 
J. &W 
J. &W 
J. &W 
J. &W 



1 Molinari, l.c. (Table V). 2 K onig, l.c. (Table V). 3 J. & W., I.e. (Table V). 
4 Mass. Exp. Sta., l.c. (Table VI). 6 Bui. 120, l.c. (Table V). 



280 ORGANIC AGRICULTURAL CHEMISTRY 

Cocoanut. — The fruit of the cocoanut palm yields a solid 
oil used mostly in making soaps but also somewhat as a food, 
the entire fleshy part of the nut being used also as food. 

Cacao. — The solid oil or fat obtained from the cacao bean 
is known as cacao butter. It is a by-product in the manu- 
facture of chocolate, etc. It is used mostly as a toilet article 
and in soap making. 

Flaxseed. — This seed is a by-product from flax grown for 
the fiber for the manufacture of linen. The oil obtained from 
the seed is known as linseed oil. It is a drying oil and is used 
in varnishes and paints. It is not a food. 

Maize. — The oil extracted from the germ of corn, separated 
in the milling of the grain, is used as an edible oil to some extent 
and also as a semi-drying oil and in making soaps. The ex- 
tracted germ meal is used as stock food. 

Fat Content of Crops. — The fat content of crops is given 
in the above table. The figures are those for the ordinarily 
determined " ether extract " and thus do not represent pure 
fat. They include other minor constituents such as waxes, 
chlorophyll and some of the organic acids. 

Lecithin and Phytosterol 

Closely associated with the fats, though not strictly classed 
with them, are two substances of considerable importance in 
both plants and animals. They are phytosterol and lecithin. 

Phytosterol and Cholesterol. — Phytosterol is a monatomic 
alcohol of high carbon content which is present in plants. The 
formula assigned to it is C27H45OH, though a phytosterol ob- 
tained from Calabar beans has been given the formula C30H47OH, 
on account of which it is distinguished as stigmasterol. Phytos- 
terol occurs in practically all vegetable fats. It is most abundant 
in pea fat and the fat of the Calabar bean. In most vegetable 
fats it amounts to 0.1-0.3 P er cent - A substance isomeric with 
phytosterol but found in animals, especially in wool fat, is 
known as cholesterol. It occurs normally in all cells, in blood 
and in lymph. It is present in largest amounts in brain and 



PLANT CONSTITUENTS — FATS, PROTEINS 281 

nerve tissue. Its occurrence here is thought to be connected 
with the other substance which we have referred to, viz. 
lecithin. It is also thought to be connected with the action 
of certain toxins. It is found in the bile, where it causes the 
formation of a certain kind of gall stone. The constitutional 
formula for these two compounds has not been fully established, 
but they are probably secondary alcohols containing both an 
unsaturated group and a hexahydrobenzene ring, and related to the 
ter penes. Therefore, without going into details, we may simply 
say that monatomic alcohols of high carbon content known 
as phytosterol and stigmasterol in plants and cholesterol in 
animals are found associated with vegetable and animal fats. 

These alcohols are non-saponifiable, so that when fats con- 
taining them are saponified they remain as unsaponifiable 
matter. In analytical determinations of fats the unsaponifiable 
matter, as usually determined, consists largely of these com- 
pounds. They are soluble in ether and in alcohol and may be 
removed from a saponified fat by extraction with ether. 

Phytosterol and cholesterol are very similar in all their 
properties and have melting points very close together. They 
cannot, therefore, be separated or identified by determining 
their melting points. They each yield an ester with acetic 
acid, however, and these esters have distinctly different melt- 
ing points which thus makes it possible to identify them. 

Cholesterol acetate m. p. ii4.3°-ii4.8° 

Phytosterol acetate m. p. i25°-i37° 

It is possible that this difference in melting point is due to the 
fact that phytosterol is not an individual compound but a 
mixture of several similar ones such as stigmasterol. 

The importance of these two compounds is mainly in the 
fact that the presence of phytosterol in a fat establishes the 
fat as of vegetable origin, while cholesterol is present only in 
animal fats. As to their food value nothing is known. It is 
probable that the cholesterol in animals is derived from the 
phytosterol in the plants which the animal uses as food. If 



282 ORGANIC AGRICULTURAL CHEMISTRY 

this is so the importance of phytosterol in plants as a source 
of cholesterol in animals is connected with the antitoxic action 
of cholesterol of which we shall soon speak. 

Lecithin. — This substance is definitely related to fats in its 
constitution, as it is an ester of glycerol. Fats, it will be recalled, 
are neutral or tri-acid esters of glycerol, i.e. all three of the 
glycerol hydroxyl hydrogens are replaced by fatty acid radicals 
Lecithin is like the fats in being a neutral or tri-acid ester but, 
while in fats all of the hydroxyl hydrogens are replaced by fatty 
acid radicals, in lecithin only two of the three are thus replaced 
by fatty acid radicals. The third is replaced by the phosphoric 
acid radical. In addition to this the phosphoric acid radical 
has one of its remaining acid hydrogens replaced by a basic 
radical of a compound known as choline. This choline is not a 
simple alcohol but is a tri-methyl-hydroxy-ethyl ammonium 
hydroxide compound. Thus in lecithin there are four distinct 
parts, viz. (a) glycerol; (b) fatty acid, usually stearic, palmitic 
or oleic; (c) phosphoric acid; (d) choline, a nitrogen (amine) 
base. On hydrolysis lecithin yields all four of these parts and 
this hydrolysis is produced enzymatically by the fat-splitting 
enzyme lipase. Lecithin belongs to a group of compounds 
known as phospho-lipines, which signifies fat-like bodies con- 
taining phosphorus and also nitrogen (amine). 

The chief source of lecithin is the yolk of eggs, from which fact 
the name lecithin is derived. It is also, like cholesterol, a normal 
constituent of the living cell and is found in blood, lymph and 
muscle tissue. It is also often associated with fats, especially 
in brain, nerve tissue and eggs. In plants it is found in the seeds 
especially of legumes and cereals. 

The amounts of lecithin in some of these substances are as 
follows : 

Egg yolk 9.4 per cent 

Liver 2.1 per cent 

Blood 1.8 per cent 

Legume seeds 0.8-1.6 per cent 

Cereal grains 0.25-0.53 per cent 



PLANT CONSTITUENTS — FATS, PROTEINS 283 

Physiological Function. — Physiologically lecithin is very 
important. We have spoken of the fact that it is hydrolyzed 
by the enzyme lipase and in the animal body the lecithin of 
plant food is probably digested and absorbed in much the 
same way as fats. If the lecithin of animals, essential to the 
living cell and nerve tissue, is derived in the case of herbivorous 
animals entirely from plant lecithin, it thus becomes an essential 
food constituent. The generally accepted connection between 
organic phosphorus (lecithin compounds) in food and the 
building of brain and nerve tissue is based upon these facts. 

We know nothing in regard to the metabolism of lecithin 
and only very little in regard to its probable function in the 
living cell. Recent work upon certain toxic substances, e.g. 
the toxins of cobra poison and of tetanus, leads to the view that 
lecithin acts as an accelerator to these toxins. Its general 
physiological action is perhaps of a like nature, that is, it acts 
as an accelerator to the activity of enzymes. We spoke of the 
fact that cholesterol acts as an antitoxin. Toward lecithin it 
acts in such a way that it prevents the accelerating action of 
lecithin upon these toxins. We thus see how intimately these 
two compounds are connected with each other, and though we 
know relatively little as yet in regard to them, their importance 
is at least indicated. 



PROTEINS 

Proteins differ from carbohydrates in not being an abundant 
constituent of plants, though they are, nevertheless, a universal 
and essential constituent. In animals, on the contrary, pro- 
teins are the abundant constituent. All protoplasmic cell 
contents of plants contain protein, and as proteins differ in 
composition from carbohydrates and fats in containing the 
element nitrogen this element becomes an essential plant food 
constituent. 

Forms of Proteins. — We have previously stated that pro- 
teins are synthesized in the leaves of plants, but they are found 



284 ORGANIC AGRICULTURAL CHEMISTRY 

in the cell contents, in cell sap, in plant juices and as reserve food 
in seeds, roots, etc. In these different localities we find proteins 
existing in three different states or forms : (1) in solution in 
the cell sap or plant juices ; (2) in crystalline form in the cell 
contents or in reserve organs; (3) in amorphous solid bodies 
as reserve food in seeds. The two solid forms, crystalline and 
amorphous, in which they occur as reserve food in seeds, roots, 
etc., may be either pure or mixed, i.e. partly crystalline and 
partly amorphous. The solid protein bodies resulting are 
known as aleuron grains. They are found in a certain layer in 
the seed known as the aleuron layer, as in castor oil bean, wheat 
grain, etc. The structure of these aleuron grains is often 
complex, but they consist usually of solid protein inclosed in a 
less soluble protein membrane and the whole body has a dis- 
tinctly granular appearance. Several different proteins may be 
present in one aleuron grain, but the most common one is a 
globulin. In most seeds the aleuron layer is directly beneath 
the outer seed coat. 

Occurrence. — Proteins occur principally in the seeds of 
plants and are most abundant in the seeds of legumes and 
cereals. Crops yielding these seeds are thus of especial im- 
• portance as food for domestic animals, for while carbohydrates 
and fats furnish the greater part of the energy value of foods 
it is from plant protein alone that herbivorous animals must 
build their own body protein. 

• In discussing>the chemical nature of proteins we stated that 
they yield amino-acids on hydrolysis. The principal amino- 
acid^ obtained from vegetable iproteins differ from those that 
are obtained from proteins of animal origin. Thus, glutaminic 
acid, proline and arginine are obtained in larger amounts from 
vegetable proteins. Also alcohol soluble proteins, e.g. gliadin 
of wheat, are found only in plants. On the other hand, some 
amino-acids are obtained only from animal proteins. These 
differences in the two classes of proteins evidently affect their 
food value, but at present we do not know enough in this regard 
to warrant further discussion. 



PLANT CONSTITUENTS — FATS, PROTEINS 



285 



TABLE X 

Protein Content of Crops 





Protein (NX 6. 25) 




Crop 
















(Fresh Basis) 


(Dry Basis) 




Cottonseed meal .... 


42.3 (40.2) 


46.1 


J. & W., pp. 12-19 1 (Mass. Exp. 
Sta., p. 46) 2 


Linseed meal (new process) 


33-2 (36.5) 


36.9 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 47) 


Linseed meal (old process) 


32.9 (33.6) 


35-2 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 47) 


Gluten meal 


41.3 (24.9) 


32.5 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 47) 


Malt sprouts 


23.2 (26.6) 


25.8 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 49) 


Wheat bran 


15.4 (16.5) 


17.4 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 51) 


Wheat middlings . . . 


15-6 (17.8) 


17.8 


J. & W., pp. 12-19 (Mass. Exp. 
Sta., p. 50) 


Germ meal 


9-8 


11.0 


J. & W., pp. 12-19 


Sesame seed (cake) . . . 


3S-4o 




Molinari, p. 591 3 


Brazil nut 


15.5 


16.5 


Konig, p. 616 4 


Peanut . . . 




27-5 


29.7 


Konig, p. 615 


English walnut 




16.7 


18.0 


Konig, p. 611 


Cowpeas (peas) 




20.8 


24.4 


J. & W., pp. 12-19 


Soja bean . . 




34-o 


38.1 


J. & W., pp. 12-19 


Oats .... 




11.8 (12.7) 


13-2 (13.8) 


J. & W., pp. 12-19 (Bull. 120, 
p. 24) 5 


Wheat (spring) 




12. 5 (i3-3) 


13.9 (14-8) 


J. & W., pp. 12-19 (Bui. 120, p. 33) 


Wheat (winter) 




11.8 (10.7) 


13. 1 (11.9) 


J. & W.,pp. 12-19 (Bui. 120.P. 33) 


Rye .... 




10.6 (12.2) 


12.0 (13-4) 


J. & W.,pp. 12-19 (Bui. 120. p.35) 


Barley . . . 




12.4 (12. 1) 


13-9 (i3-4) 


J. &W.,pp. 12-19 (Bui. i20,p.36) 


Sorghum . . 




9.1 (10.3) 


10.4 (11. 7) 


J.&W.,pp. 12-19 (Bui. 120, p. 42) 


Maize (flint) . 




10.5 


11.8 


J. & W., pp. 12-19 


Maize (sweet) 




12.8 


14.0 


J. & W., pp. 12-19 


Rice .... 




7-4 


8.5 


J. & W., pp. 12-19 


Alfalfa, grass . 




4.8 


17. 1 


J. & W., pp. 12-19 


Alfalfa hay 




14-3 


15.6 


J. & W., pp. 12-19 


Red clover, grass 




4.4 


iS-3 


J. & W., pp. 12-19 


Red clover hay 




12.3 


14-5 


J. & W., pp. 12-19 


Timothy grass 




3-1 


8.0 


J. & W., pp. 12-19 


Timothy hay . 




5-9 


6.8 


J. & W., pp. 12-19 


Maize fodder (cured) . . 


4-5 


7.8 


J. & W., pp. 12-19 


Maize stover (cured) . . 


3-8 


6.5 


J. & W., pp. 12-19 


Maize stalks (cured) . . 


i-9 


59 


J. & W., pp. 12-19 


Potatoes 


2.1 


IO.I 


J. & W., pp. 12-19 


Sweet potatoes 




1-5 


5-2 


J. & W., pp. 12-19 


Turnips . . • 




1.1 


12.4 


J. & W., pp. 12-19 


Mangels . . 




1.4 


15.2 


J. & W., pp. 12-19 


Rutabaga . . 




1.2 


10.4 


J. & W., pp. 12-19 


Red beets . . 




i-5 


13-4 


J. & W., pp. 12-19 


Sugar beets . 




1.8 


130 


J. & W., pp. 12-19 



ij. &W., I.e. (Table V). 
' 3 Molinari, Z.c. (Table V). 

5 Bui. 120, I.e. (Table V). 
protein. 



2 Mass. Exp. Sta., I.e. (Table VI). 
4 Konig, I.e. (Table V). 
In this bulletin the factor N X 5-7 is used for wheat 



286 ORGANIC AGRICULTURAL CHEMISTRY 

Protein Content of Crops. — The protein content of some of 
the different crops is given in the preceding table. The figures 
represent crude protein as determined by multiplying the 
nitrogen per cent by the factor 6.25. This includes, with the 
proteins, the amino-acids, but these are not of any large amount 
except in the cases of green crops and root crops and in malt 
sprouts. 



AMINO-ACIDS, ALKALOIDS, ESSENTIAL OILS, TER- 
PENES, TANNINS, ETC. 

We have thus far discussed the occurrence in plants of the 
three essential organic food constituents together with a few 
related compounds of industrial or physiological importance. 
These are by far the most important plant constituents, es- 
pecially from an agricultural viewpoint, for plants considered 
agriculturally are chiefly used as food. When not used as 
food they are generally used for the manufacture of valuable 
products. All of these uses have been as fully considered as 
is desirable. 

There remain, however, several groups of substances found in 
plants which are of considerable importance. 

End Products of Metabolism. — In animal metabolism pro- 
teins are broken down by the katabolic process into simpler 
compounds with the liberation of energy. The nitrogen-con- 
taining compounds which are thus formed are carried off in 
the urine, as true excretion products, in the form of urea and 
related compounds. In plants protein cell food is probably 
katabolized in a similar way, but the nitrogen-containing prod- 
ucts are not cast off from the plant as true excretion substances. 
It is possible that amino-acids are excreted as such, but in many 
cases these amino-acids or other complexes derived from the 
protein molecule are not excreted, but are further metabolized 
into end products which remain in the plant. Such charac- 
teristic compounds as caffeine, theobromine, strychnine, morphine , 



PLANT CONSTITUENTS — FATS, PROTEINS 287 

skatol, indigo, and certain essential oils like vanillin, are without 
doubt formed in this way. 

Amino-acids. — In regard to the occurrence of amino-acids 
themselves in plants it may be stated that about eight have 
been isolated. A recent view in regard to the occurrence of these 
acids and other probable products of protein metabolism in 
plants and soil is, that these excretion products, when present 
in the soil, act as toxins to the plant itself. As previously 
stated also (p. 250) amino-acids in the soil may, in some cases, 
be used by plants as a direct source of nitrogen for the synthesis 
of plant protein. The amino-acids present in the plant itself 
also function in the resyn thesis of plant protein. 

Alkaloids, Essential Oils, Terpenes, Tannins, etc. — Of these 
different groups of compounds some are of importance medici- 
nally, some have a very great value as perfumes, etc., and others 
in various ways. They include substances known as alkaloids, 
e.g. quinine, morphine (from opium), nicotine, strychnine, 
brucine, etc. These are all valuable medicines. Also sub- 
stances known as essential oils, e.g. oil of peppermint, oil of 
cloves, oil of rose, heliotrope, vanillin (vanilla), etc. These are 
used as constituents of perfumes or flavors and some of them 
also medicinally. Then we have the group known as terpenes, 
including lemon oil, turpentine and camphor, and finally the 
tannins, used in leather manufacture and obtained from the 
bark of hemlock, oak and other trees. 

These various compounds belong mostly to the more complex 
groups of organic compounds and in most cases are physiolog- 
ically related to the plant as end products of metabolism, as 
just discussed. They are of great economic value, and the plants 
producing them are grown as agricultural crops in certain more 
or less restricted localities. In general, however, they are not 
important agriculturally. 



CHAPTER XVII 

ANIMAL FOODS AND FEEDING 

FOOD VALUE 

In the study of the physiological processes of plants and 
animals we have brought out the following general facts. By 
utilizing the energy of the sunlight, living plants manufacture 
carbohydrates out of the simple substances carbon dioxide and 
water, which are present in the atmosphere and the soil. These 
photosynthesized carbohydrates by further metabolic changes in 
the plant are transformed, in part, into the vegetable fats and, 
with the assistance of nitrogen compounds obtained in most 
cases from the soil in the form of nitrates, are in part transformed 
into proteins. In this way the plant builds up its own food 
supply and stores up a reserve supply of food for its offspring. 
This reserve food may also become a source of food for animals. 
These essential organic food constituents all possess potential 
energy which, through the processes of animal metabolism, be- 
comes converted into the kinetic energy of animal heat or 
muscular work. This intimate relation between plants and 
animals is the important one of food and nutrition. 

In our study of animal physiology we discussed the processes 
by which these food constituents — carbohydrates, fats and pro- 
teins — were digested and then metabolized in order to yield the 
energy of animal life. The chemical reaction involved in the 
liberation of this energy is that of oxidation brought about 
by the process of respiration, by which the oxygen of the air 
is brought into contact with the digested, assimilated and 
partially metabolized food materials. 

Quantitative Relation of Food to Energy. — We have now to 
consider the quantitative relation of this food to the energy of the 

288 



ANIMAL FOODS AND FEEDING 289 

living animal, that is, the relation between the food eaten and the 
result produced in the form of energy. In the case of domestic 
animals, however, with the exception of the horse and other 
draft animals, the ultimate production of energy is not the 
only result to be obtained by feeding. In all young growing 
animals a part of the food is used for the building of body 
substance, and this is also true of sheep, cows and poultry or 
other animals producing wool, milk, eggs, etc. In the case of 
fattening animals, also, part of the food is used for the produc- 
tion of stored body fat. Whether the food, however, is used 
entirely for the production of energy or partly for building 
body protein or storing body fat, the value of the food is always 
measured in terms of energy. 

Digestibility of Food Constituents 

In considering the relation of food to the energy produced, 
i.e. the value of the food, the first factor to be taken account of 
is the digestibility, or the amount of the different food materials 
actually digested in the animal body. If we consider pure food 
constituents, that is, pure carbohydrates, pure fats or pure 
proteins, it might seem natural to suppose that the animal 
body would completely digest and absorb each constituent. 
Yet, it will not be surprising to know that, even under the most 
favorable conditions, the animal body is not thus able to digest 
all of any pure food constituent. In all cases the amount 
digested is something less than 100 per cent. 

Coefficient of Digestibility. — Thus we have for each food 
constituent what is termed the coefficient of digestibility, which 
expresses the percentage amount of the food constituent which 
the animal does actually digest and absorb. For example, 
the human body, when fed carbohydrate food in the form of 
starch in cooked cereal grains or as bread, is able to digest ap- 
proximately 98 per cent of it. This figure, then, is the coefficient 
of digestibility for carbohydrate food in this form for man. 

This coefficient of digestibility is determined directly, by 



290 



ORGANIC AGRICULTURAL CHEMISTRY 



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a?i^a§g 

C/5 ^ ;§ ;§ ;=| C/5 C/2 o 

. "a3 <u <u . . „cj 



ANIMAL FOODS AND FEEDING 291 

experiment, by subtracting from the amount of food eaten the 
amount present in the faecal excrement, as it is in this excrement 
that the undigested food material remains. 

The digestibility of a food constituent will vary also according 
to the condition in which it is fed, as, for example, whether it 
is mixed with a large amount of other material, or, in the case 
of human foods, whether it is raw or cooked. While this is 
important, it does not alter the actual amount digested so 
much as it does the rapidity or ease of digestion. In general, 
the coefficients of digestibility refer to a food constituent in the 
usual form in which it is eaten. For man therefore the coef- 
ficient of digestibility of starch refers to cooked starch, while 
for domestic animals it refers to raw starch as present in cereal 
grains, etc. For cattle the average digestibility of starch in 
corn or wheat is almost as high as for man, viz. 92-95 per cent, 
while in other animal foods, such as oats and hay, the diges- 
tibility of nitrogen-free extract falls as low as 62 per cent and 
with horses and sheep from 47 to 62 per cent. 

We see, therefore, that the particular species of animal and 
even the particular individual animal may possess a different 
coefficient of digestibility. To obtain absolute figures therefore 
for the coefficients of digestibility a great deal of experimenta- 
tion is required. We can, however, take certain average re- 
sults and use them in calculating the digestibility of foods and 
their food value. 

Without going more into detail the data in the preceding table 
represents the average results of experimental evidence on the 
subject. 

Application of Coefficients of Digestibility. — From these 
coefficients of digestibility we can readily calculate, from the 
percentage composition of a food, the exact amount of each of 
the food constituents which an animal actually digests. The 
following examples will illustrate : 



2 Q2 



ORGANIC AGRICULTURAL CHEMISTRY 









^U33 I3J 


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q q h 








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g 


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to to to 




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ft 

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On t^OO 


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«~ £ CU 












J4 CO .2 

















ANIMAL FOODS AND FEEDING 293 

Thus, with any food of which an analysis has been made, we 
can determine the amount digested, provided we have coefficients 
of digestibility which apply. In some cases where the identical 
food or animal has not been subject to experiment it is necessary 
to use the data most nearly corresponding; e.g. wheat for 
horses, in the table of coefficients, is given as "figures obtained 
with oats." 

Energy Value of Food Constituents 

Having then determined the amount of food constituents 
which an animal digests, the next step is to find out how much 
energy this digested food will yield. We have previously said 
that whether animal food yields energy directly or is used to 
build body substance, eventually, in most cases, the final result 
is energy, as the body substance is later torn down and energy 
is set free. Also that whether this energy is manifested as heat 
or as muscular work, the units for expressing the energy are 
always in terms of heat. The liberation of energy in the 
animal body is by the reaction of oxidation and this reaction is 
easily carried out in accurate physical apparatus which allows 
the exact determination of the energy liberated. In such re- 
actions the substance burns and the heat produced by this 
burning is the measurement of the energy of the substance. 

Fuel Value. — This we term the combustion value or fuel 
value of the substance, and this fuel value, which we express in 
heat units, represents the energy value which, in a food substance, 
means the food value. Therefore the fuel value of a food con- 
stituent or any substance used as food is equivalent to its pos- 
sible food value. 

Bomb Calorimeter. — This determination of the fuel value or 
food value of food substances is made in a piece of apparatus 
known as a bomb calorimeter. Speaking very generally, this 
consists of a heavy thick- walled metallic cylinder or bomb. 
This is so constructed that a substance placed within it may 
be ignited and burned, usually in pure oxygen gas under pres- 
sure, and the heat generated by this combustion is determined 



294 ORGANIC AGRICULTURAL CHEMISTRY 

by measuring the rise in temperature accurately to .ooi° C. 
which takes place in a large volume of water in which the 
bomb is immersed. 1 

Calorie. — The rise in temperature produced by the com- 
bustion is calculated in units of heat energy known as calories. 
A calorie is the amount of heat necessary to raise the temperature 
of i.o gram of water i° C. In the absolute calorie unit this rise 
of temperature is from 15 C. to 16 C, but the unit may be 
defined in slightly more general terms, as first given. This 
unit is small and in practice is multiplied by 1000 ; i.e. it is the 
heat necessary to raise 1000 g. of water i° C. To distinguish 
these two units they are termed respectively the small calorie 
or gram calorie, written without capitals, and the large calorie 
written capitalized or Calorie. Still a third unit has been 
suggested by Armsby known as the Therm (T.), which is equiva- 
lent to 1000 Calories or 1,000,000 gram calories. This is used 
mostly in calculating large feeding rations of domestic animals. 
In calculating human foods the unit usually employed is the 
Calorie (large calorie). In English standards the Calorie is 
approximately equivalent to the amount of heat necessary to 
raise 1 pound of water 4 F. 

Thus the Calorie is the unit in which the energy value or 
food value of a food is expressed. It will often be found referred 
to in other terms, as we have mentioned, viz. fuel value, calorific 
value or heat of combustion. All of these terms are, therefore, 
synonymous as applied to foods, with the corrections which 
we shall now consider. 

Fuel Values in Calories. — What then are the fuel values in 
Calories of the three food constituents? While all figures 
determined do not agree exactly, the ones usually accepted at 
present are as follows : 

1 gram Carbohydrates yields 4.1 Cal. 
1 gram Fats yields 9.45 Cal. 

1 gram Proteins yields 5.65 Cal. 

1 A detailed description of this apparatus may be found in U. S. Dept. Agr. O. E. 
S. Bui. 21 (1895), or in J. Am. Chem. Soc, XXV, 659 (1903). 



ANIMAL FOODS AND FEEDING 295 

These are the results which have been obtained in the bomb 
calorimeter. If, therefore, these food constituents are burned 
in the animal body in a similar manner as in the calorimeter, 
then these figures apply directly to that portion of the food that 
is actually digested. 

Corrected Fuel Values. — In discussing the metabolism of 
these constituents we showed that in the case of carbohydrates 
and fats the processes in the body and in the calorimeter are 
similar ; i.e. the constituents are in both cases completely oxidized 
to carbon dioxide and water. The figures for these two constit- 
uents hold therefore for the digestible portion. In the case of 
proteins, however, katabolism does not yield the simple products 
of oxidation which are obtained by burning in the calorimeter. 
Part of the products of the katabolism of proteins are the complex 
nitrogen compounds excreted in the urine, and these compounds 
still contain some of the potential energy of the original proteins. 
It has been found that the amount of energy contained in these 
excretion products, and thus not liberated when proteins are 
burned in the body, is equivalent to approximately 1.3 Cal. per 
gram of protein. The fuel value of proteins, as obtained in the 
calorimeter, must be reduced therefore by this amount, so that, 

Fuel value (in bomb) of proteins 5.65 Cal. — 1.3 Cal. 
= 4.35 Cal. = fuel value (in body) or food value 

The corrected values then become, 

1 gram digested Carbohydrates yields in body 4.1 Cal. 
1 gram digested Fats yields in body 9.45 Cal. 

1 gram digested Proteins yields in body 4.35 Cal. 

Metabolizable or Available Energy. — In man the coefficients 
of digestibility have been determined on the average mixed diet, 
and as human beings probably differ less in these coefficients 
than do different species of animals, it is possible to apply these 
coefficients not to each food and each individual but once for all 
to the food values in calories. Doing this, we obtain the follow- 
ing: 



296 



ORGANIC AGRICULTURAL CHEMISTRY 



1 gram Carbohydrates, as eaten, yields 98 per cent of 4.1 = 

4.0 Cal. 
1 gram Fats, as eaten, yields 95 per cent of 9.45 = 9.0 Cal. 
1 gram Proteins, as eaten, yields 92 per cent of 4.35 = 4.0 Cal. 

These figures represent the energy in Calories which the 
human body actually uses, i.e. which is available for metaboliza- 
tion from each gram of the constituent as eaten. These results 
have been designated by different names, viz. physiological fuel 
value, metabolizable energy or available energy. The figures given 
are for man and are in Calories per gram. Similar data have 
been obtained for domestic animals, and it is also often desirable 
to express them in English standards, viz. Calories per pound. 
In all calculations for the conversion of grams into pounds, 
453.6 grams = 1 pound. 1 

The following table gives all of these data together : 



TABLE XIII 

Fuel Values of Food Constituents 





Calories per Gram 


Constituent 


In Bomb 


In Body 
Digest. Part 


In Body, Food as Eaten 
(Physiological, Metabo- 
lizable, Available) 




Man 


Dog 


Carbohydrates 

Fats 


4.1O 
9-45 
5.6S 


4.IO 
9-45 
4-35 


4.0 
9.0 

4.0 


4.1 
9-3 


Proteins 


4.1 




Calories per Pound 


Carbohydrates 

Fats 


i860 
4286 
2562 


i860 
4286 
1973 


1814 
4082 
1814 


i860 
4218 


Proteins 


i860 



Fuel Values for Cattle. — In working with cattle and other 
ruminants, Kellner 2 found that the values obtained with dogs 

1 U. S. Bureau of Standards, Tables of Equivalents (1906). 

2 "Die Ernahrung der landw. Nutztiere," 1912. 



ANIMAL FOODS AND FEEDING 297 

were too high. His conclusions and average results are as 
follows : 

Carbohydrates, 1 chiefly starch and crude fiber, are subject to 
losses in metabolizable energy due to bacterial fermentation 
with the formation of methane which is excreted with the faeces. 
With crude fiber this loss approximates 13.7 per cent of the fuel 
value of the digested nutrient, even amounting to as much as 
20 per cent in the case of wheat straw. With 4.184 Cal. per 
gram as the total fuel value of starch and crude fiber, the above 
loss reduces this to about 3.6 Cal. per gram. The presence of 
other carbohydrates (pentosans and some sugars) gives a result 
from experimental data of 3.761 Cal. per gram as the metaboliz- 
able or available fuel value for the digestible carbohydrates (em- 
bracing nitrogen-free extract, crude fiber and pentosans) in 
ordinary cattle foods. 

Fats 2 do not suffer loss by bacterial fermentation and their 
metabolizable energy is the same as their fuel value. In 
analysis, however, the fats are determined as ether extract and 
this ether extract contains other substances than pure fats, e.g. 
waxes, chlorophyll, etc., which have a different fuel value and 
are not metabolized as fats. This results in the metabolizable 
value of the ether extract being considerably less than the fuel 
value. The ether extract of meadow hay and cereals has a fuel 
value of 9.194 Cal. per gram, while the metabolizable energy of 
the digestible nutrient equals only 8.322 Cal. per gram. 

Proteins 3 with a fuel value of 5.778 Cal. per gram corrected 
for loss of energy in the urine constituents, as previously ex- 
plained, have a metabolizable value of digestible nutrient equal 
to 4.697 Cal. per gram. 

Putting these results together in a table with the equivalents 
in Calories per pound we have as the best data for the metabo- 
lizable or available energy of the digestible nutrients in ordinary 
cattle foods the following : 

1 "Die Ernahrung der landw. Nutztiere," 191 2, pp. 88-95. 

2 l.c, pp. 87-88. 8 I.e., pp. 80-85. 



298 



ORGANIC AGRICULTURAL CHEMISTRY 



TABLE XIV 
Fuel Values of Food Constituents for Cattle (Kellner) 



Constituent 


Calories per Gram of Digestible 
Nutrient 




Fuel Value 


Metabolizable 
Energy 


Carbohydrates 

(N-free ext, crude fiber, pentosans) 
Fats (ether extract) (in hay) .... 
Proteins 


4.183 

9.194 
5.778 


3.761 

8.322 
4.697 




Calories per Pound of Digestible 

Nutrient 


Carbohydrates 

Fats 

Proteins 


1897 
4170 
2621 


1706 

3775 
2130 



FOOD REQUIREMENT 

Energy Requirement 

Maintenance Requirement. — The energy represented by 
these figures is the amount per gram or pound of actually 
digested nutrient which cattle are able to utilize in metabolism. 
This energy is either liberated in the form of body heat or 
muscular work, the latter being both the involuntary work of 
the body and the voluntary work of labor ; or, the equivalent 
nutrient is stored as body substance (mostly fat), in case it is 
in excess of the energy demands of the body. 

The energy which it is necessary to supply in food for the 
purpose of maintaining the life of the animal (body heat + in- 
voluntary muscular work) is known as the maintenance require- 
ment and a ration which supplies this only is termed a main- 
tenance ration. 

The energy of this maintenance requirement is expended in 
performing the essential operations of the body and keeping 



ANIMAL FOODS AND FEEDING 299 

it in a certain condition. It may be divided somewhat as 
follows, in the case of man : 

Maintaining body heat and muscular tone . . 40 per cent 

Respiration 20 per cent 

Circulation 10 per cent 

Digestion and assimilation 12 per cent 

Other involuntary muscular work . . . . 18 per cent 

The total amount of energy thus required has been deter- 
mined in the case of both man and domestic animals. The 
following may be taken as average results. 

A man of 150 lbs. at rest requires approximately 2000 Cal. 
per day. 

A steer of 1100 lbs. (500 Kg.) requires for maintenance 
approximately 12,000 Cal. per day. 

All of the energy of the food in excess of this maintenance 
requirement is utilized by the body in (1) voluntary muscular 
work, (2) production of body substance (increase in weight). 

Respiration Calorimeter. — Experiments to carefully deter- 
mine the relation between the energy of the food and the energy 
utilized by the body in maintenance and in doing work or 
increasing weight have been carried out in what is known as 
the respiration calorimeter. This consists of a large box in which 
a man or animal may live under very accurately controlled 
conditions such that all food and air used and all excretion 
products, heat produced and muscular work performed are 
determined. As a result of these experiments, performed on 
man in this country by Atwater and Benedict, and on animals 
by Armsby, and in Europe by Rubner, Zuntz, Kellner and 
others, it has been fully established that the law of the con- 
servation of energy applies to the utilization of food in the 
animal body, i.e. all of the energy of the food actually metab- 
olized is utilized in one of the ways mentioned. 

Production Value. — The energy that is in excess of the 
maintenance requirement is thus productive in that it produces 



300 ORGANIC AGRICULTURAL CHEMISTRY 

either additional muscular work or body material, and the value 
of the food for this purpose is termed the production value. 

In the normal mature man the production of increased body 
weight is not desired, and all of the productive energy of food 
is available for increased muscular work. In horses this same 
fact is true. In fattening cattle, however, and in swine, milch 
cows, sheep and poultry, the production value of foods is 
utilized for increase in body weight or for the building of ma- 
terial which is being constantly withdrawn by man, the volun- 
tary work requirement being practically nothing. 

Energy Requirement for Man. — Taking results that have 
been obtained by Atwater, Benedict and others for the production 
energy necessary for various degrees of work in man, we have : 

Energy Requirement of Normal Adult Man 150 Lbs. Wt. 

At rest (maintenance), about 2000 Cal. per day. 

Moving about but no active work, about 2300 Cal. per day. 

Moving about and light work, about 2500 Cal. per day. 

Moving about and moderate work (carpenter), about 3000 
Cal. per day. 

Moving about and active work (farmer), about 3500 Cal. per 
day. 

Moving about and very active work (excavator), about 4500 
Cal. per day. 

Moving about and extreme work (lumberman), about 5000 or 
over Cal. per day. 

These results are obtained by figuring a man's day as composed 
of various activities incident to it, e.g. 8 hours' sleep, at 65 Cal. 
per hour; 2 hours for meals, going to and fro, at 170 Cal. per 
hour ; 6 hours' sitting, at 100 Cal. per hour ; 8 hours of labor, 
170 to 600 Cal. per hour, depending upon degree of activity. 

We thus see that the production requirement for man ranges 
from 300 to 3000 Cal. per day. 

It may be mentioned that all efforts to determine the energy 
expended in even the most severe mental and nervous work have 
failed. 



ANIMAL FOODS AND FEEDING 



30I 



Production Values for Cattle. — In fattening cattle the 
productive energy results in increase in body weight, and this 
factor as well as the Calorie unit has been used as the measure 
of such energy. The term used is pounds of flesh gained, which 
is not exactly equivalent to increase in live weight, as the latter 
includes water. 

When fed in addition to a basal maintenance ration each of 
the food nutrients has been found to possess a certain production 
value. This value is not, however, in proportion to the relative 
metabolizable energy values of the same nutrients. Expressed 
in Calories Kellner 1 has found that the following are the 
results : 

TABLE XV 

Metabolizable Energy and Production Energy of Nutrients 





Metabolizable 
Energy 


Production Energy 


Nutrient 


Cal. per 
Gram 


Cal. per 
Pound 


Cal. per 
Gram 


Cal. per 
Pound 


Pounds 
Flesh 
Gained 

per 
Pound 


Carbohydrates 2 

(N-free Ext. Crude Fiber Pentosans) 
Fats (Ether extract) 3 (in hay) . . . 
(in cereals) . . 
Proteins 


3.761 

8.322 
8.322 
4..607 


1706 

3775 
3775 
2130 


2.36 

4-50 
5.oi 
2.24 


1070 

2041 
2273 
IOl6 


.248 

•474 
.526 
•235 







Summary. — Let us summarize what has been said in regard 
to digestibility and energy values by means of a table giving the 
results for three of our common animal foods as fed to fattening 
cattle. 

1 " Die Ernahrung der landw. Nutztiere," p. 159. 

2 The values for sugar are less than for starch and crude fiber, viz. .188 pounds 
flesh gained. 

3 The values for fats (ether extract) in concentrates like cottonseed meal and in 
cereal grains is greater than for hay. Production value for oil foods equals .598 
pounds flesh gained, for grains .526 pounds flesh gained. The latter value applies 
to the total ether extract of ordinary mixed foods. 



302 



ORGANIC AGRICULTURAL CHEMISTRY 



TABLE XVI 

Digestibility and Energy Values of Three Animal Foods per ioo 
Pounds of Food 

(Based upon Kellner's figures for cattle as already quoted) 



Nutrient 



gg 



lis 

< n u 
P 2 g 



w a 



Production Value 



5 W -i 

o 3 < 



Carbohydrates 
(Nitrogen - free extract 

and pentosans) 
Crude Fiber 
Fats .... 
Proteins . . . 
Totals . . 



Carbohydrates 
(Nitrogen - free extract 

and pentosans) 
Crude Fiber 
Fats .... 
Proteins . . . 
Totals . . 



Carbohydrates 
(Nitrogen - free extract 

and pentosans) 
Crude Fiber 
Fats .... 
Proteins . . . 
Totals . . 



66.29 

12.20 

4-33 

I3-76 



96.58 



78.72 
2.78 
2.36 

14.20 



98.06 



81.96 
2.21 
4.40 
9-9i 



98.48 



Oats 



50.38 
3-42 
3-46 

10.73 



67.99 



95,571 

6,488 

14,428 

28,123 



85,948 

5,835 

13,062 

22,855 



144,610 127,700 76,333 17.68 



53,907 
3,659 
7,865 

10,902 



Wheat 



72.42 
1.30 
1.49 

n-93 



87.14 



I37,38i 

2,466 

6,213 

31,269 



123,549 

2,218 

5,625 

25,4H 



177,329 156,803 94,388 21.86 



77,489 
i,39i 
3,387 

12,121 



Maize 



77.86 
1.28 
3-92 
7.14 



90.20 



147,700 

2,428 

16,346 

18,714 

185,188 



132,829 

2,184 

14,798 

15,208 



165,019 



83,310 
i,370 
8,910 
7,254 



100,844 



12.49 
0.85 
1.82 
2.52 



17.96 
0.32 
0.78 
2.80 



19-31 
0.32 
2.06 
1.68 



23-37 



Nutritive Ratio. — The results for the fuel value of the three 
food constituents have led to the use of a factor, especially in 
connection with feeding rations of domestic animals, which 



ANIMAL FOODS AND FEEDING 303 

though perhaps not as valuable as originally thought, or at 
least in the sense first given to it, is yet often used. This is 
known as the nutritive ratio and expresses the ratio, calculated 
directly from the amounts present, between the proteins and the 
other two constituents. It will be observed that, approximately, 
the protein and carbohydrates are equal in food value while 
fats are 2.25 times as large. If the amount of fat food is multi- 
plied by 2.25, it is then in equivalent terms to the other two. 
If we make the following proportion : 

Amount protein : (Amount carbohydrates + amount fats X 2.25) 

: : 1 : x, 

then 1 : x will represent the ratio of the protein constituents to 
the other two. This is termed the nutritive ratio. In a general 
way the results of feeding depend upon this ratio, for when x 
is large, e.g. 8 to 12, the ratio is usually a fattening one and 
is termed broad, whereas when it is small, e.g. 4 to 7, the ratio 
is not fattening but still supplies the energy requirements of 
animals, especially for work, and is termed narrow. In the 
broad nutritive ratio it will be observed the carbohydrates 
and fats which produce body fat are in large proportion, while 
in the narrow ratio they are small. 

Protein Requirement 

In discussing the maintenance requirement we have spoken 
only of the energy factor. Not only does the animal body 
require a certain amount of energy to be supplied in its food, but 
there must also be in it a certain minimum amount of protein. 
As food protein is absolutely essential to the formation of body 
protein, the torn-down muscle tissue must be replaced by protein 
supplied in the food. The energy represented in this protein 
metabolism is part of the total energy requirement, but aside 
from this there must be in the food a certain amount of protein 
considered solely as building material. This may be illustrated 
by the fact that while the necessary maintenance requirement 
of 2000 Cal. per day for man, or 12,000 Cal. per day for steers, 



304 ORGANIC AGRICULTURAL CHEMISTRY 

might be easily supplied by carbohydrates and fats alone, yet, 
except for a brief period, such non-protein food is unable to 
supply the needs of the body because torn-down body protein 
is impossible of reconstruction. In adult man or in non-fatten- 
ing or non-producing mature animals the amount of protein in 
the body does not increase. All of the protein food is thus 
indirectly converted into energy, but in the process it first serves 
as a constructing substance and cannot be wholly replaced by 
either of the other food constituents. 

The amount of the protein requirement in man is a question 
over which there has been considerable controversy. The 
standard usually accepted from studies of normal diets and of 
the nitrogen income and outgo of normal men has been 100 
grams of protein per day for a man of 150 pounds. Some in- 
vestigators, however, especially Chittenden, reduce this amount 
to as low as 70 grams or even less. 

We have given figures showing the effect of increased muscular 
activity upon the energy requirement of the body, raising the 
amount from 2000 Cal. per day for maintenance to 5000 Cal. 
per day under severe muscular exertion. In contrast to this is 
the fact that increased muscular activity has only a slight effect 
upon the amount of protein metabolism. On the other hand, 
while increased food supply raises the energy metabolism of the 
body only slightly, it has the direct and marked effect of increas- 
ing the protein metabolism. That is, an increase in protein 
food increases the amount of protein metabolized, there being 
no appreciable increase in the amount of body protein. An in- 
crease in carbohydrate and fat food increases the general 
metabolic action, which in turn increases the amount of body 
protein torn down in the muscular activity of the accompanying 
physiological processes. 

In the foregoing discussion we have considered only the main 
facts in regard to the value of foods and the food requirements 
of the body. The actual value and economic use of foods, the 
effect of varying conditions upon the food requirements and the 
fixing of standard or feeding rations have all been omitted as 



ANIMAL FOODS AND FEEDING 305 

pertaining more to a study of the practice of feeding than to a 
general presentation such as has been the purpose of this book. 
Enough has been considered both in regard to plant and 
animal physiology and foods to give to the student a general 
but definite and scientific knowledge of the topics discussed. 

References, Section III 

Atwater, Chemistry and Economy of Food (U. S. D. A. ; O. E. S. 

Bui. 21), 1895. 
Atwater, Foods, Nutritive Value and Cost (U. S. D. A. Bui. 23), 1894. 
Atwater and Bryant, Composition of American Food Materials 

(U. S. D. A.; O. E. S. Bui. 28), 1899. 
Armsby, Principles of Animal Nutrition, 19 10. 
Armsby, Available Energy of Timothy Hay (IT. S. D. A. ; O. E. S. 

Bui. 51), 1903. 
Allen, Feeding of Farm Animals (U. S. D. A. Bui. 22), 1901. 
Chamberlain, Feeding Value of Cereals (U. S. D. A. ; Bur. Chem. 

Bui. 120), 1909. 
Haywood et al., Commercial Feeding Stuffs (U. S. D. A. ; Bur. Chem. 

Bui. 108), 1908. 
Jenkins & Winton, Compilation of Analyses of American Feeding 

Stuffs (U. S. D. A.; O. E. S. Bui. 11), 1892. 
Jordan & Hall, Digestibility of American Feeding Stuffs (U. S. D. A. ; 

O. E. S. Bui. 77), 1900. 
Kellner, Die Ernahrung der landw. Nutztiere, 1912. 
Kellner, Grundzuge der Fiitterungslehre, 1908. 
Langworthy, Function and Uses of Food (U. S. D. A. ; O. E. S. Bui. 

46). 
Sherman, Food Products, 1914. 
Wiley, Cereal and Cereal Products (U. S. D. A. ; Bur. Chem. Bui. 13, 

IX), 1898. 
Wiley, Analysis of Cereals (U. S. D. A.; Bur. Chem. Bui. 45), 1895. 
Wiley, Composition of Maize (U. S. D. A. ; Bur. Chem. Bui. 50), 1898. 



INDEX 



Absorption, of food, 160, 183, 188. 
Acetaldehyde, 144. 

experiments, 46. 
Acetamide, 82. 
Acetic acid, 46, 47, 49. 

experiments, 51. 

glacial, 49. 

properties of, 49. 

salts of, 49. 
Acetic acid series, table, 47. 
Acetic fermentation, 50. 
Acetylene, 24, 133. 
Acetylene series, 133. 
Achroodextrin, 124, 166. 
Acid-amides, 55, 82. 
Acid-chlorides, 55. 
Acid-nitriles, 21. 
Acids, 46-53, 67-81. 

derivatives of, 54-65. 

of milk, 210. 

polycarboxy, 51. 

saturated and unsaturated, 134. 
Acrolein, 133. 
Acrylic acid, 133. 
Acrylic aldehyde, 133. 
Activators, 143. 
Adipocellulose, 125, 265. 
Aerobic bacteria, 250. 
Agar-agar, 272. 
Alanine, 85. 
Albumin, 89. 

egg, 88, 91. 

preparation of, for experiments, 

Heller's ring test for, 230, 231. 

in urine, 230. 

serum, 202. 

toxic, 205. 
Albuminoids, 89. 
Albuminuria, 230. 
Alcohol, 26, 31. 

absolute, 36. 

denatured, 38. 

from carbohydrates, 34, 39, 121, 1 

industrial uses of, 37. 

per cent, table, 28. 

source of, 121. 

taxation of, 37. 



i74 



26. 



Alcoholic beverages, 36. 
Alcoholic fermentation, 32. 

experiments, 34. 
Alcohols, 25-41. 

derivates of, 54-65. 

dihydroxy, 41. 

experiments, 26, 27, 31, 34, 40. 

higher, 39, 41. 

oxidation products of, 42-53. 

polyhydroxy, 40. 

table, 26. 

trihydroxy, 41. 
Aldehyde, 44. 
Aldehydes, 42, 45. 

addition compounds, 44. 

experiments, 45. 

reactions of, 44. 
Ale, 36. 

Aleurone grains, 284. 
Aleurone layer, 284. 
Alimentary canal, 163. 
Alkaloids, 286. 
Alkyl halides, 18. 
Allyl alcohol, 133. 
Allyl aldehyde, 133. 
Aluminium, in plants and animals, 147. 
Amidulin, 166. 
Amines, 21. 
Amino-acetic acid, 83, 84. 

ammonium salt of, 84. 

hydrochloride, 84. 
Amino-acids, 82, 85, 91, 286. 

from protein digestion, 201. 

in plants, 284, 286, 287. 

in soil, 249, 287. 
Amino-butyric acid, beta methyl, 85. 
Amino-caproic acid, 86. 
Amino-glutaric acid, 86. 
Amino-propionic acid, 85. 

beta hydroxy, 86. 

beta hydroxy-phenyl, 87. 

beta indol, 87. 

beta phenyl, 86. 
Amino-succinic acid, 86. 

amide, 86. 
Amino-valeric acid, beta methyl, 86. 

delta guanidine, 87. 

307 



3 o8 



INDEX 



Amino-valeric acid, (Continued) 

gamma methyl, 86. 
Amino compounds in soil, 249, 287. 
Amino-formamide, 97. 
Amino-formic acid, 97. 
Amino-group, 11. 
Ammo-methane, 22. 
Ammonia, derivatives, 22. 

in urine, 228. 
Ammonium amino-formate, 98. 
Ammonium carbamate, 98. 
Ammonium carbonate, 98. 
Ammonium citrate, 80. 
Ammonium cyanate, 99. 
Amygdalin, in. 
Amyl alcohols, 39. 
Amyl valerate, 56. 
Amylases, 145. 
Amyloid, 125. 
Amylopsin, 122, 145, 170. 
Anaesthetics, 18. 
Aniline dyes, 135. 
Animal food, 159, 190, 288. 
Animal heat, 233. 
Animal nutrition, 159, 190. 
Animals, liberation of energy by, 236. 

physiological processes of, 158. 
Anti-en2ymes, 144, 225. 
Antithrombin, 225. 
Apple juice, 113. 
Arabinose, no. 
Arabitol, 41. 
Arachidic acid, 47, 58. 
Arginine, 87, 284. 
Argol, 76. 
Armsby, 294, 299. 
Arterial blood, 193. 
Arsenic, in plants and animals, 147. 
Ash, 149. 
Asparagine, 86. 
Aspartic acid, 86. 
Assimilation, in plants, 238. 
Assimilatory pigment, 238. 
Asymmetric carbon, 71. 

theory of, 71. 
Atwater, 299. 
Available energy, of foods, 295. 

Babcock test, 211, 215. 
Bacteria, aerobic, 250. 

denitrifying, 253. 

nitrate, 250. 

nitrogen-assimilating, 250. 

nodule, 250. 



Baking powder, 77. 
Barley sugar, 116. 
Beer, 36. 
Beeswax, 57. 
Benedict, 299. 

Fehling's solution modified by, 230. 
Benzaldehyde, in. 
Benzene, 135. 
Benzine, 135. 
Benzol, 135. 

Benzoyl amino-acetic acid, 84, 92. 
Benzoyl glycine, 92. 
Bile, 181, 182. 
Bioses, 108. 
Biuret, 101. 

preparation of, 102. 
Biuret reaction, 96. 
Blood, 209, 219-226. 

action of snake venom on, 225. 

arterial, 193, 221. 

carbohydrates in, 192. 

clotting of, 223, 224. 

constituents of, 220. 

corpuscles, 220, 222. 

defibrinated, 225. 

dust, 220. 

experiments, 226. 

glucose in, 192, 193, 223. 

hemagglutination in, 220. 

haemogloblin, 89, 220. 

haemolysis in, 220. 

inorganic constituents, 223. 

laking of, 221. 

organic constituents of, 223. 

oxygen-carrying power of, 222. 

oxy haemoglobin, 91, 221. 

plasma, 199, 220, 223. 

properties of, 220. 

serum, 91, 223. 

stroma, 220. 
Brandy, 37. 
Brazil nut, 277. 
Bright's disease, 230. 
Buchner, 33, 140. 
Building material in plants, 246. 
Butane, 13, 15. 

isomerism of, 16. 
Butter, 216. 

composition of, 217. 
Butterine, 217. 
Butyric acid, 47, 58, 74, 210. 

Caffeine, 103, 286. 
Cagniard de la Tour, 32. 



INDEX 



309 



Calcium, as plant food, 152. 

in plants and animals, 147. 
Calcium carbide, 24. 
Calcium cyanamide, 23. 

experiments, 25. 
Calorie, 294. 

large, 294. 

small, 294. 
Calories, fuel value in, 294. 
Calorific value, 293. 
Calorimeter, bomb, 293. 

respiration, 299. 
Camphor, 287. 
Cane sugar, 108, 115-118. 

action of yeast on, 116. 

action on Fehling's solution, 116. 

experiments, 120. 

hydrolysis of, 117. 

in vegetables, etc., 116. 

occurrence of, 115. 

optical activity of, 116. 

properties of, 116. 
Capric acid, 47, 58, 210. 
Caproic acid, 47, 210. 
Caprylic acid, 47, 210. 
Caramel, 116. 

Carbocyclic compounds, 135. 
Carbohydrates, 87, 104-130. 

absorption of, 183. 

classification of, 107, 109. 

composition of, 104, 155. 

compound, 107. 

constitution of, 105. 

conversion into fats, 195. 

digestibility of, 290. 

digestion of, 163-17 1. 
by pancreatic juice, 170. 
in mouth, 165. 
in small intestine, 170. 
in stomach, 169. 

final digestion products of, 171. 

fuel value of, 294-296. 

function of, in plants, 241. 

in blood, 192, 193, 223. 

in milk, 209. 

in plants, 238-248. 

in portal vein, 183. 

metabolism of, in animals, 191-198. 
in plants, 242. 

metabolizable energy of, 295-298. 

respiratory quotient of, 197. 

simple, 107. 

summary, 130. 

table, 129. 



Carbon, in plants and animals, 147. 
Carbon dioxide, assimilation of, 238. 
Carbon monoxide, in photosynthesis, 239. 
Carbon tetrachloride, 19. 

experiments, 19. 
Carboxyl, 46. 

Casein, 74, 88, 173, 210, 212. 
Caseinogen, 173, 211. 
Castor oil bean, 277. 
Catalytic, 32, 33, 139. 
Cattle, food values for, 2g6. 

production values for, 301. 
Cattle foods, digestibility of, table, 302. 
Cell, animal, 154. 

composition of, 154. 

fundamental chemical reactions of, 

157- 

living, 154. 

plant, 154. 
Cell energy, 155, 156. 
Cell food, 154-158, 243, 251 
Cell wall, 247. 
Celluloid, 127, 263. 
Cellulose, 108, 120, 125-128. 

adipo, 265. 

alcohol from, 39. 

as food, 265. 

compound, 262. 

digestibility of, 265. 

experiments, 128. 

forms of, 262. 

hemi, 262, 263. 

hexanitrate of, 127. 

hydrolysis of, 125, 128. 

in plants, 247, 252, 262. 
experiments, 267. 

ligno, 264. 

normal, 262. 

pecto, 264. 
Cellulose content of crops, table, 266. 
Cellulose explosives, 127, 263. 
Cereal plants, 269. 
Cerebron, 114. 
Cheese, 212, 217. 
Cherry gum, no. 
Chewing, 161. 
Chloracetic acid, 67. 
Chloral, 67, 
Chloral hydrate, 67. 
Chlorides, as plant food, 152. 
Chlorine, in plants and animals, 147. 
Chlormethane, 11. 
Chloroform, 18. 

experiments, 19. 



3io 



INDEX 



Chlorophyll, 147, 238. 
Chlorophyll bodies, 238. 
Chloroplasts, 238. 
Cholesterol, 220, 223, 280. 
Cholesterol acetate, 281. 
Choline, 282. 
Chyme, 176. 
Cider, 49. 
Citric acid, 80. 

experiments, 80. 
Clotting of blood, 224. 
Coagulating enzymes, 142, 173. 
Coal, 6. 
* Coal tar, 135. 

Coal tar dyes, 135. 
Coefficients of digestibility, 289, 
291. 

table, 290. 
Coenzymes, 144. 
Cognac, 37. 
Collodion, 128, 263. 
Cologne spirits, 36. 
Columbian spirits, 29. 
Combined acid, 167, 174. 
Combustion value, 293. 
^ Constitutional formula, 8. 
; *£ Corn sirup, 34, 123. 

• V« Cotton, 125, 262. 

• "* analysis of, 263. 

> ^^mercerized, 127, 263. 
» "^Cottonseed, 277. 

• •XZream of tartar, 76. 
Creatinine, 97, 288. 
[rops, 259. 
' cellulose content of, table, 266. 

fat content of, table, 279. 
\ % protein content of, table, 285. 
• starch content of, table, 269. 

sugar content of, table, 276. 
Crotonic acid, 133. 
Crotonic aldehyde, 133. 
Crude fiber, 126, 265. 

determination of, 267. 
Crude tartar, 76. 
Curd, 212. 
Cutin, 125, 265. 
Cyanamide, 23. 
Cyanides, 21. 

experiments, 25. 
Cyanogen group, 11. 

Decane, 13. 
Decapeptides, 92. 
Denitrifying bacteria, 253. 



290, 



♦ ^Jr 



Dextrin, 120, 124, 271. 
Dextro-rotatory, 70. 
Dextrose, in, 112. 
Diabetes, in, 229. 

Diastase, 33, 34, 120, 122, 140, 145, 
244. 

experiments, 246. 

of secretion, 245. 

of translocation, 245. 
Di-brom-ethane, symmetrical, 20. 

unsymmetrical, 20. 
Diethyl carbonate, 99. 
Dihalogen ethanes, 20. 

isomerism of, 20. 
Digestibility of food, 289-293. 

table, 302. 

coefficients of, 289. 
Digestion of food, 159-183. 
Digestion and absorption, resume* of, 

186. 
Digestive region, 163. 
Digestive tract, 163. 
Dioxy stearic acid, 210. 
Dipeptides, 92. 
Disaccharoses, 108, 115-119. 

experiments, 120. 

hydrolysis of, 115, 164. 
Distillation, destructive, 29. 

fractional, 27. 
Distilled liquors, 37. 
Duct of Wirzung, 176. 
Dulcitol, 41. 
Duodenum, 176. 

Edestin, 91. 
Egg albumin, 91. 
Eicosane, 13. 

Electrical fixation of atmospheric nitro- 
gen, 251. 
Emulsion, 145. 
Enantiomorphic crystals, 79. 
Endothermic reactions, 235. 
Energy, kinetic, 233. 

organisms liberating, 233, 236. 

potential, 233. 

source of, in plants, 237. 

storage of, by plants, 236. 
Energy food, of plants, 251. 
Energy requirement, 298, 300. 
Energy value, of foods, 293, 295. 

table, 302. 
Enterokinase, 144, 145, 177. 
Enzyme, definition of, 140. 

meaning of, 139. 



INDEX 



311 



Enzyme action, catalytic nature of, 139. 

character of, 142. 

reversibility of, 143. 

specificity of, 142. 
Enzymes, 33, 130-145- 

amy lory tic, 141. 

coagulating, 142, 173. 

decomposing, 142. 

fat-hydrolyzing, 141. 

glucoside-hydrolyzing, 141. 

hydrolyzing, 141. 

lipolytic, 141, 180. 

names of, 144. 

nature of, 140. 

oxidizing, 142. 

protein-hydrolyzing, 141. 

proteolytic, 141, 173. 

reactions brought about by, 141. 

reducing, 142. 

saccharolytic, 141. 

salivary, 166. 

splitting, 142. 

starch-hydrolyzing, 141. 

sugar-hydrolyzing, 141. 

table, 145. 
Erepsin, 145, 178. 
Erythritol, 41. 
Erythrocytes, 220, 223. 

number of, 222. 

size of, 222. 
Erythrodextrin, 124, 166. 
Esophagus, 163. 
Essential oils, 286. 
Esterification, 58. 

experiments, 62. 
Esters, 56. 

experiments, 55, 62. 

properties of, 54. 
Ethane, 13, 15. 

synthesis of, 13. 
Ethereal salts, 56. 
Ethers, 54. 
Ethyl acetate, 56. 
Ethyl alcohol, 26, 31-39. 

experiments, 31. 

properties, 31. 

test for, 32. 

test for water in, 32. 
Ethyl amino-formate, 98. 
Ethyl ether, 34. 

experiments, 55. 
Ethyl halides, 19. 
Ethylene, 132. 
Ethylene bromide, 20, 132. 



Ethylene series, 133. 
Ethylidene bromide, 20. 
Excretion, 160. 
Exothermic reactions, 235. 
Experiment studies, I, Hydrocarbons from 
wood and coal, 7. 
II. Methane, 9. 

III. Halogen substitution prod- 

ucts, 19. 

IV. Cyanides, 25. 

V. Alcohols, distillation, 26. 
VI. Methyl alcohol, 30. 
VII. Ethyl alcohol, 31. 
VIII. Alcoholic fermentation, 34. 
LX. Amyl alcohol, 40. 
X. Aldehydes, 45. 
XL Formic acid, 48. 
XII. Acetic acid and vinegar, 51. 

XIII. Oxalic acid, 53. 

XIV. Ether, 55. 
XV. Esters, 62. 

XVI. Fats and soaps, 63. 
XVII. Lactic, malic, tartaric and 

citric acids, 80. 
XVIII. Proteins, 93. 
XLX. Urea, 101. 

XX. Carbohydrates, general prop- 
erties, 105. 
XXL Pentosans and pentoses, no. 
XXII. Hexoses, 114. 
XXIII. Disaccharoses, 120. 
XXW. Starch, 123. 
XXV. Cellulose, 128. 
XXVI. Organic and inorganic con- 
stituents, 152. 
XXVII. Salivary digestion, 168. 
XXVIII. Gastric digestion, 174. 
XXLX. Milk, 218. 
XXX. Blood, 226. 
XXXI. Urine, 231. 
XXXII. Diastase and starch, 246. 
XXXIII. Cellulose and crude fiber, 

267. 
XXXIV. Starch, 270. 
XXXV. Pentosans, 273. 
Explosives, 127. 

Fats, 57-65. 
absorption of, 185. 
as food, 277. 
body, 199. 

chemical constants of, 61. 
composition of, 155. 
conversion into carbohydrates, 200. 



312 



INDEX 



Fats, (Continued) 

digestibility of, 290. 

digestion of, 179-183. 

experiments, 64. 

final digestion products of, 181. 

fuel value, 294. 

hydrolysis of, 179. 

important, 60. 

in blood plasma, 199. 

in crops, 277-280. 

in plants, 248, 249, 277. 

metabolism of, 198. 

metabolizable energy of, 298. 

milk, 199, 210. 

physical constants of, 61. 

properties of, 64. 

respiratory quotient of, 197. 

saponification of, 60. 
experiments, 63. 

synthesis of, in plants, 248. 

table, 62. 
Fatty acids, 57. 

of milk fat, 210. 
Fehling's solution, 77, 112. 

Benedict's, 230. 
Fermentation, 139. 

alcoholic, 32-35. 
Ferments, 33, 140. 

organized, 33, 140. 

unorganized, 33, 140. 
Ferric ammonium citrate, 80. 
Fertilizers, commercial, 152. 
Fibrin, 223, 224. 
Fibrin enzyme, 224. 
Fibrinogen, 223, 224. 
Fire damp, 8. 

Fire-extinguishing liquids, 19. 
Flax, 125. 
Flaxseed, 277. 
Food, absorption of, 183-188. 

and energy, 288, 293-303. 

animal, 159-208, 288-305. 

as building material, 157. 

definition of, 159. 

digestibility of, 289-293. 
table, 292, 302. 

digestion and absorption of, 159-183. 

energy, 155. 

energy value of, 293-303. 

fuel value of, 293. 

function of, 157, 234. 

oxidation of, 156. 

plant, 234, 241-257. 

production value of, 299. 



Food, (Continued) 

reserve in plants, 244. 

utilization of, 160. 
Food materials, essential organic, 146. 
Food passage, time for, 188. 
Food requirements, 298. 
Food value, 288. 
Foods and feeding, 288-305. 
Formaldehyde, 42. 

as disinfectant, 43, 46. 

as food preservative, 43, 216. 

experiments, 45. 

from carbon dioxide and water, 43. 

in photosynthesis, 239. 

uses of, 43. 
Formalin, 43. 
Formic acid, 46-48. 

experiments, 48. 

in photosynthesis, 239. 
Fractional distillation, 27. 
Fructose, 106, in, 113, 275. 

optical activity of, 113. 

synthesis of, 114. 
Fruit flavors, 56. 
Fruit sugar, in, 113, 275. 
Fuel value of foods, 293-298. 

corrected, 295. 

for cattle, 296, 298. 

table, 296, 298. 
Furfural, no. 

Galactans, 114, 264, 271, 272. 
Galactose, in. 
Gall bladder, 163. 
Gastric lipase, 180. 
Gastric juice, 33, 172. 

as germicide, 174. 

enzymes in, 172. 

experiments, 174. 

hydrochloric acid in, 172, 173, 174. 
Germ, 245. 

Germination, in plants, 245. 
Germ meal, 277. 
Gin, 37- 
Gliadin, 284. 
Globulins, 89. 
Glucosans, 271. 
Glucose, 35, 106, in, 223, 275. 

action on Fehling's solution, 112, 114. 

determination, in. 

fermentation of, 113. 

from other carbohydrates, 113. 

in blood, 192. 

in plants, 275. 



INDEX 



313 



Glucose, (Continued) 

in urine, 111, 229, 231. 

occurrence and properties of, in. 

optical activity of, 113- 

oxidation of, in body, 193. 

photosynthesis of, 114, 239. 

reduction of silver solution by, 114. 

source of, 123. 

synthesis of, 114. 
Glucose sirup, 112. 
Glucosides, in. 
Glutaminic acid, 86, 284. 
Gluten, wheat, 88. 
Glycerin, 41. 
Glycerol, 41, 109. 
Glycerol esters, 58. 
Glycerose, 109, 114- 
Glyceryl tripalmitate, 60. 
Glycine, 84. 
Glycocholic acid, 182. 
Glycogen, 120, 121, 124, 192, 271. 

amount in liver, 192. 

conversion into glucose, 192. 

muscle, 194. 
Glycol, 40. 

ethylene, 41. 
Glycolic aldehyde, in photosynthesis, 240. 
Glyco-proteins, 89, 168. 
Glycosuria, 229. 
Glycyl-glycine, 92. 
Grape juice, 113. 
Grape sugar, in, 275. 
Green plants, 238. 
Gum arabic, no, 272. 
Gums, 247, 272. 
Gum tragacanth, 272 
Guncotton, 127. 

soluble, 128. 

HEMAGGLUTINATION, 220. 

Haemoglobin, 89, 147. 

blood, 89, 220. 
Haemolysis, 220. 
Halogen-acids, 67. 
Halogen-aldehydes, 66. 
Halogen-ethanes, 19. 
Halogen-methanes, 18. 
Hard water, experiments, 64. 
Heat, and work, 156. 

body, 157- 
Heliotrope, 287. 
Heller's ring test, 230, 231. 
Hemp, 125, 262. 
Hepatic vein, 192. 



Heptane, 13. 
Heptoses, 108. 
Hexacontane, 13, 15. 
Hexane, 13, 15. 
Hexoses, 108, 110-115. 

experiments, 114. 
Hippuric acid, 84, 92. 

in urine, 229. 
Honey, in. 
Hormones, 176. 
Humus, 249. 
Hydracrylic acid, 68. 
Hydrazones, 107. 
Hydrocarbons, 5. 

from wood and coal, experiments, 7. 

saturated and unsaturated, table, 133. 

synthesis of higher, 13. 

table, 13. 
Hydrochloric acid, in gastric juice, 174. 

combined, 174. 
Hydrogen, in plants and animals, 147. 
Hydrogen peroxide, in photosynthesis, 

230- 
Hydrolysis, 59. 

experiments, 63. 
Hydroxy -acids, 67. 
Hydroxy-propionic acids, 68. 
Hydroxy substitution products, 65. 
Hydroxyl, 25. 

Immunity, 144. 
Indigo, 287. 
Insecticides, 49. 

Intestinal juice, carbohydrate, digestion 
by, 170. 

protein digestion by, 175, 178. 
Intestine, large, digestion in, 182. 

small, 163, 175. 
fat digestion in, 180. 
protein digestion in, 175. 
Intestines, digestion in, 187. 
Inulin, 125, 271. 
Inversion, 117. 
Invertase, 116. 
Invert sugar, 117. 
Iodoform, 18. 

experiments, 19. 
Iron, in plants and animals, 147. 
Isoleucine, 86. 
Isomaltose, 167. 
Isomerism, 15. 

space, 17. 

stereo, 17. 

structural, 16. 



3i4 



INDEX 



Isopropyl iodide, 16. 

Jute, 262. 

Karo corn sirup, 34> 123. 

Katabolism, 190. 

Kellner, 299. 

Kinase, 143. 

Kjeldahl method, 90, 215. 

calculations of, 95. 

Gunning modification of, 94. 

reactions of, 94. 

Lactalbumin, 211, 212. 
Lactase, 145, 171. 
Lactic acid, 68, 210. 

dextro, 69, 74. 

experiments, 80. 

from milk sugar, 119. 

from sour milk, 79, 119. 

inactive, 73. 

levo, 74. 

sarco, 74, 223. 

space formula of, 72. 
Lactic acid bacteria, 73, 74, 210. 
Lactic acid fermentation, 69. 
Lactide, 74. 
Lactoglobulin, 211. 
Lactometer, 215. 
Lactose, 115, 119, 209. 

action on Fehling's solution, 119. 

fermentation of, 1 19. 

optical activity of, 119. 
Laurie acid, 74, 210. 
Le Bel, 71, 78. 
Lecithin, 220, 223, 280, 282. 

amount in plants and animals, 282. 

physiological function of, 283. 
Lemons, 80. 
Leucine, 86. 
Leucocytes, 220, 222. 

number of, 222. 
Levo rotatory, 70. 
Levulosans, 271. 
Levulose, 111, 113. 
Liebig, 32. 
Lignin, 125, 247. 
Lignocellulose, 125, 264. 
Limes, 80. 
Lime-nitrogen, 24. 
Linen, 125, 262. 
Linolenic acid, 61. 
Linolic acid, 61, 134. 
Lipases, 145, 180. 



Liver, 121, 192. 
Lock and key theory, 143. 
Lymph, 219. 
Lymphatic system, 198. 
Lysine, 82. 

Magnesium, as plant food, 152. 

citric acid salt of, 56. 

in plants and animals, 147: 
Maintenance ration, 298. 
Maintenance requirement, 298, 299. 
Mafic acid, 75. 

experiment, 80. 
Malt, 118, 120. 

Maltase, 35, 120, 123, 145, 165, 171, 244. 
Maltose, 35, 115, 118, 167, 275. 

action on Fehling's solution, 118. 

f ermentati on of, 118. 

in plants, 275. 

optical activity of, 118. 
Malt sugar, 115, 118. 

action on Fehling's solution, 118. 

fermentation of, 118. 

optical activity of, 118. 
Man, energy requirement for, 300. 
Mannans, 264, 271, 272. 
Mannitol, 41. 
Manure, 152. 
Marsh gas, 7. 
Mastication, 161. 
Mercerized cotton, 127. 
Metabolism, 160, 190-208. 

direct, 191. 

end products of, in plants, 286. 
Metabolizable energy, of foods, 295. 
table, 301. 

of carbohydrates, 298. 

of fats, 298. 

of proteins, 298. 
Methane, 7, 13, 15. 

constitution of, 6, 8. 

experiments, 9. 

occurrence of, 7. 

properties of, 8. 
Methane series, table, 13. 
Methyl alcohol, 26, 27, 29. 

experiments, 30. 

from beet sugar residues, 29. 

from wood, 29. 

properties of, 30. 

source of, 29. 

use of, 30. 
Methyl amine, 12, 22. 
Methyl ammonium chloride, 23. 



INDEX 



315 



Methyl bromide, 12. 
Methyl chloride, 12. 
Methyl cyanide, 12. 
Methyl halides, 13. 
Methyl hydroxide, 12. 
Methyl iodide, 12. 
Milk, 119, 209-216. 

American, 215. 

analysis, 215. 

average, 214. 

ash of, 214. 

constituents of, 209. 

experiments, 218. 

extreme variations in, 214. 

fat of, 210. 

fat-rich, 214. 

food value of, 218. 

general properties of, 214. 

inorganic constituents of, 212. 

proteins of, 215. 

preservatives of, 216. 

salts of, 212. 

souring of, 119, 210. 

standard, 214. 

sugar in, 119, 209. 

total solids of, 213, 214. 
Milk sugar, 115, 119. 

action on Fehling's solution, 119. 

fermentation of, 119. 

optical activity of, 119. 
Millon's reaction, 95. 
Millon's reagent, 95. 
Mixed compounds, 66. 
Mono-chlor methane, 12. 
Mono-halogen ethanes, 19. 
Monosaccharoses, 107, 109-115. 

final products of digestion, 164. 
Moore's test, 105. 
Morphine, 286. 
Mouth, 163, 186. 
Mucin, 89, 168. 
Muscular work, 233. 
Myristic acid, 47, 210. 

Natural gas, 6. 

Nephritis, 230. 

Nicotine, 287. 

Nitrate bacteria, 250. 

Nitrates, as plant food, 152, 249. 

in soil, 249. 
Nitrides, 251. 

Nitrogen, atmospheric, in fertilizers, 
24. 

electrical fixation of, 251. 



Nitrogen, (Continued) 

excretion of, 205. 

fixation of atmospheric, 251. 

in plants and animals, 147. 

Kjeldahl method for, 90. 

of katabolized protein, 205. 

organic, in soil, 249. 

source of, in plants, 249, 252. 
Nitrogen-assimilating bacteria, 250. 
Nitrogen cycle, 250. 

diagram of, 255. 

reactions of, 254. 
Nitro group, n. 
Nodule bacteria, 250, 252. 
Nonoses, 108. 
Normal salt solution, 221. 
Nucleo proteins, 89. 
Nutrition, animal food and, 159-208. 

Octadecapeptides, 92. 
Octoses, 108. 
Oil, cacao, 280. 

castor, 278. 

coconut, 280. 

cottonseed, 278. 

flaxseed, 280. 

linseed, 280. 

maize, 280. 

olive, 278. 

palm, 278. 

peanut, 278. 

sesame, 278. 
Oil of bitter almonds, in. 

cloves, 287. 

garlic, 134. 

lemon, 287. 

mustard, 134. 

peppermint, 287. 

rose, 287. 

turpentine, 287. 
Oils, plant and animal, 57-65, 277-280. 

table, 62. 
Oleic acid, 61, 133, 134, 210. 
Oleomargarine, 217. 
Olive oil, 277. 
Optical activity, 69. 
Oranges, 80. 

Organic chemistry, definition of, 5. 
Oxalic acid, 52. 

experiments, 53. 
Oxidases, 145. 
Oximes, 44, 107. 
Oxygen, in plants and animals, 147. 

evolution, in plants, 240, 



316 



INDEX 



Oxyhemoglobin, 193, 221. 

Palmitic acid, 47, 58, 210. 
Pancreas, 163. 

Pancreatic juice, digestion of carbohy- 
drates by, 170. 

digestion of fats by, 180. 

digestion of proteins by, 175-176. 

enzymes in, 177. 

properties of, 177. 
Paper, 126, 263, 264. 

parchment, 126, 128. 
Paraffins, 10. 
Pasteur, 32, 140. 
Pectins, 125, 247. 
Pectocellulose, 125, 264. 
Pentane, 13, 15. 
Pentosans, no, 247, 264, 272. 

determination of, 273. 
Pentoses, 108, no. 
Pepsin, 33, 140, 143, 145, 173- 

action of, 174. 
Pepsinogen, 143, 173. 
Peptones, 172, 173. 
Peristaltic action, 176. 
Petroleum, 6. 
Phenylalanine, 86. 
Phenylhydrazones, 45. 
Phosphates, as plant food, 152. 
Phospholipines, 282. 
Phosphoproteins, 89. 
Phosphorus, in plants and animals, 147. 
Photosynthesis, 237-241. 

products of, 238, 241. 
Physiological salt solution, 221. 
Phytosterol, 280. 
Phytosterol acetate, 281. 
Plant physiology, 232-256. 
Plants, agricultural, 261. 

building material in, 246. 

cell food of, 243, 251. 

end products of metabolism in, 286. 

energy food of, 251. 

inorganic food of, 152. 

physiological processes of, 158. 

reserve food in, 244. 

soil food of, 250. 

source of energy of, 237. 

storage of energy by, 236. 
Plants and animals, compared, 157, 232. 

composition of, 146. 

differences between, 235. 

organic and inorganic constituents, 
146. 



Plants and animals, (Continued) 

similarity of, 232. 

volatile and nonvolatile constituents, 
147. 
Polariscope, 70. 
Polarized light, 70. 
Polypeptide nucleus, 184, 202. 
Polypeptides, 92, 172. 
Polysaccharoses, 108, 120-128. 

hydrolysis of, 120, 164. 
Portal vein, 183, 192. 

carbohydrates in, 192. 
Potassium, as plant food, 152. 

in plants and animals, 147. 
Potassium acid tartrate, 76. 
Potassium antimonyl tartrate, 77. 
Potassium palmitate, 60. 
Potassium tartrate, 76. 
Process butter, 217. 
Production value, 299. 

for cattle, 301. 
tables, 301, 302. 
Prolamines, 89. 
Proline, 284. 
Proof spirit, 38, 82. 
Propane, 13, 15. 

synthesis of, 14. 
Propionic acid, 47. 
Propyliodide, 15, 16. 
Prosecretin, 176. 
Proteases, 145. 
Protein food, 203. 
Protein requirement, 303. 
Proteins, 23, 82, 87-97. 

absorption of, 184. 

analysis of, 90. 

blood, 203. 

body, 203. 

color reactions of, 95. 

composition of, 90, 155. 

conversion of, into carbohydrates, 206. 
into fat, 207. 

chemical properties of, 90. 

determination of, 93. 

digestibility of, 290. 

digestion of, 1 71-179. 
in intestine, 175. 
products of, 178. 

experiments, 93. 

forms of, in plants, 283. 

fuel value of, 294. 

hydrolysis of, 91. 

in crops, 283, 285. 

in plants, 248, 249, 252, 283, 284. 



INDEX 



317 



Proteins, (Continued) 

katabolic products of, 204. 

katabolism of, 204. 

metabolism of, 201-208. 

metabolizable energy of, 298. 

milk, 211. 

molecular weight of, 90. 

nitrogen of katabolized, 205. 

non-nitrogenous portion of, 206. 

occurrence in plants, 284. 

oxidation of, in body, 203. 

physical properties of, 88. 

precipitation tests for, 96. 

solubility of, 93. 

synthesis of, in body, 203. 

test for nitrogen in, 93. 
Proteoses, 172, 173. 
Prothrombin, 224. 
Protoplasm, 88, 154. 
Ptyalin, 33, 121, 140, 145, 165, 166. 
Purine, 102. 

dihydroxy, 103. 

trihydroxy, 103. 
Purine bases, 97, 102. 
Pyroligneous acid, 29, 50. 
Pyroxylin, 128. 

Racemic acid, 79. 
Racemic compounds, 79. 
Radicals, 12. 
Raffinose, 108. 
Red corpuscles, 220. 
Reductases, 145. 
References, Section I, 135. 

Section II, 257. 

Section III, 305. 
Rennet, 212. 
Rennin, 145, 173, 177, 212. 

action of, 175. 
Renovated butter, 217. 
Reserve food in plants, 244. 
Resins, 247. 
Resorption, 183. 
Respiratory quotient, 196, 197. 
Rhamnose, no. 
Rochelle salts, 77, 112. 
Rubner, 299. 
Rum, 37. 

Saliva, 33» 121, 122. 
action of, 165, 167. 
alkalinity of, 167. 
amount of, 165. 
digestion of carbohydrates by, 165. 



Saliva, (Continued) 

enzymes of, 166. 

experiments, 168. 

organic substances in, 168. 

properties of, 165. 

salts in, 167. 

stimulation of flow of, 165. 
Salivary glands, 165. 
Saponification, 60. 
Sarcolactic acid, 223. 
Schweitzer's reagent, 126. 
Secretin, 176. 
Seidlitz powder, 77. 
Serine, 86. 

Serum albumin, 202, 223, 224. 
Silage, 74. 

Silk, artificial, 127, 263. 
Skatol, 287. 

Smokeless powder, 127. 
Snake venom, 225, 283. 
Soap, 60. 

experiments, 63. 

properties of, 64. 
Sodium, as plant food, 152. 

in plants and animals, 147. 
Sodium bicarbonate, 77. 
Sodium hypobromite solution, 101. 
Soil food, of plants, 250. 
Sorbitol, 41, 106. 
Sorghum cane, 116, 274. 
Space isomerism, 69. 
Spermaceti, 57. 
Starch, 35, 108, 120, 121-124, 267-270. 

acid hydrolysis of, 123. 

action on Fehling's solution, 121. 

action of saliva on, 169. 

as food, 268. 

determination of, 123. 

enzymatic hydrolysis of, 122. 

experiments, 123, 270. 

fermentation of, 120. 

hydrolysis of, 122. 

hydrolysis of, in germination, 120. 

industrial uses of, 268. 

in crops, 268. 

in plants, 244. 

iodine test for, 122. 

occurrence, 121. 

properties of, 121. 

salivary digestion of, 166. 

soluble, 166. 
Starch grains, 122. 
Starch paste, 122. 
Steapsin, 145, 180. 



3i8 



INDEX 



Stearic acid, 47, 210. 
Stereo-chemical formula, 9. 
Stereo-isomerism, 69. 
Stigmasterol, 280. 
Still, rectifying, 36. 
Stomach, 163. 

acidity of, 169. 

digestion in, 186. 

digestion of proteins in, 172. 

digestion of fats in, 180. 
Stout, 36. 

Stroma, blood, 220. 
Structural formula, 8. 
Strychnine, 286. 
Substitution, 10. 
Substitution products, 11. 
Succinic acid, 53. 

dihydroxy, 76. 

monobrom, 75. 

monohydroxy, 75. 
Sucrase, 116, 145, 171. 
Sucrose, 11 5-1 18. 

action on Fehling's solution, 116. 

action of yeast on, 116. 

experiments, 120. 

hydrolysis of, 117. 

in crops, 274, 276. 

occurrence, 115. 

optical activity of, 116. 
Succus entericus, 178. 
Sugar, 115-118, 274-276. 

analysis, 118. 

beet, 115, 274. 

cane, 115, 274. 

in crops, 274-276. 

in plants, 243. 

maple, 116, 274. 
Sulphates, as plant food, 152. 
Sulphur, in plants and animals, 147. 
Sun, as source of energy, 237. 

Tables, I. Alcohol per cent and specific 
gravity, 28. 
II. Fats and oils, 62. 

III. Summary of carbohydrates, 

129. 

IV. Enzymes, 145. 

V. Volatile and nonvolatile con- 
stituents of plants,'i5o-isi. 

VI. Cellulose content of crops, 266. 

VII. Starch content of crops, 269. 

VIII. Sugar content of crops, 276. 

DC. Fat content of crops, 280. 

X. Protein content of crops, 285. 



Tables XL Coefficients of digestibility, 
290. 
XII. Digestibility of foods, 292. 
Xni. Fuel values of food constitu- 
ents, 296. 
XTV. Fuel values and metaboliz- 
able energy for cattle, 298. 
XV. Production values for cattle, 

301. 
XVI. Digestibility and energy 
values for cattle, 302. 
Tannins, 286. 
Tartar, 76. 
Tarter emetic, 77. 
Tartaric acid, 76-78. 
dextro, 78. 
experiments, 80. 
levo, 78. 
meso, 78. 
racemic, 78. 
stereo-isomerism of, 78. 
Taurocholic acid, 182. 
Terpenes, 286. 
Tetanus toxin, 283. 
Tetra-chlor -methane, 18. 
Tetrahedral theory, 72. 
Tetrapep tides, 92. 
Tetroses, 108. 
Theobromine, 103, 286. 
Therm, 294. 
Thrombin, 224. 
Toxic albumin, 225. 
Translocation material, in plants, 243. 
Tri-chlor-aldehyde, 66. 
Tri-chlor-methane, 18. 
Tri-iodo-me thane, 18. 
Trioses, 108, 109. 
Tripeptides, 92. 
Trisaccharoses, 108. 
Trypsin, 143, 145, 177. 

hydrolytic action of, 178. 
Trypsinogen, 144, 177. 
Tryptophane, 87. 
Turpentine, 287. 
Tyrosine, 87. 

Unsapontfiable matter, 281. 
Unsaturated compounds, 130-134. 
Urea, 82, 97-101. 

determination of, 101. 

experiments, 101. 

formation of, 100. 

in blood, 223. 

in body, 205. 



INDEX 



319 



Urea, (Continued) 

in saliva, 168. 

in soil, 249. 

in urine, 100, 227. 

isolation of, from urine, 227, 231. 

synthesis of, 99. 
Ureometer, 101. 
Uric acid, 82, 97, 102, 103, 223, 228. 

in blood, 223. 

in urine, 228. 
Urine, 209, 226-231. 

albumin in, 230. 

ammonia in, 228. 

constituents of, 227. 

creatinine in, 228. 

distribution of nitrogen in, 229. 

experiments, 231. 

general properties of, 230. 

glucose in, in, 229. 

hippuric acid in, 229. 

isolation of urea from, 227. 

nitrogen compounds in, 227. 

nitrogen excretion in, 205. 

pathological constituents of, 229. 

total nitrogen of, 205. 

urea in, 227. 

uric acid in, 228. 

Valeric aced, 47. 
Valine, 85. 
Vanilla, 287. 
Vanillin, 287. 
van't Hoff, 71, 79. 
Vegetable ivory, 272. 
Vinegar, 50. 
experiments, 51. 



Volatile and nonvolatile constituents, 
147. 

experiments, 152. 

in plants, table, 150. 
von Schwann, 32. 

Water, assimilation of, in plants, 

238. 
Waxes, 57. 

in plants, 277. 

table, 62. 
Westphal balance, 215. 
Wheat bran, 1 10. 
Whey, 212, 217. 
Whisky, 37. 

White corpuscles, 220, 222. 
Wine, 36. 

Wirzung, duct of, 176. 
Wohler, 99. 
Wood alcohol, 26, 29. 
Wood gum, no. 
Wood vinegar, 50. 
Work, and heat, 157. 

muscular, 157, 233. 

Xanthine, 97, 103. 

dimethyl, 103. 

trimethyl, 103. 
Xanthoproteic reaction, 96. 
Xylose, no. 

Yeast, 32, 113. 

Zuntz, 299. 
Zymase, 32, 113, 145. 
Zymogens, 143. 



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